migration/qemu-file: Fix maybe uninitialized on qemu_get_buffer_in_place()

Fixed error when compiling migration/qemu-file.c with -Werror=maybe-uninitialized
as shown here:

../migration/qemu-file.c: In function 'qemu_get_buffer_in_place':
../migration/qemu-file.c:604:18: error: 'src' may be used uninitialized in this function [-Werror=maybe-uninitialized]
  604 |             *buf = src;
      |             ~~~~~^~~~~
cc1: all warnings being treated as errors

Signed-off-by: Wainer dos Santos Moschetta <wainersm@redhat.com>
113 jobs for migration_maybe-unitialized in 85 minutes and 35 seconds (queued for 3 seconds)
latest
Status Name Job ID Coverage
  Containers
passed amd64-alpine-container #991045186

00:02:28

passed amd64-centos7-container #991045187

00:02:44

passed amd64-centos8-container #991045188

00:02:36

passed amd64-debian10-container #991045190

00:02:38

passed amd64-debian11-container #991045191

00:02:10

passed amd64-fedora-container #991045195

00:03:42

passed amd64-opensuse-leap-container #991045203

00:02:42

passed amd64-ubuntu-container #991045202

00:02:48

passed amd64-ubuntu1804-container #991045200

00:02:40

passed amd64-ubuntu2004-container #991045201

00:03:07

passed cris-fedora-cross-container #991045194

00:02:22

passed docker-edk2 #991045184

00:01:18

passed docker-opensbi #991045185

00:01:24

passed i386-fedora-cross-container #991045196

00:02:32

passed win32-fedora-cross-container #991045198

00:02:51

passed win64-fedora-cross-container #991045199

00:02:35

passed xtensa-debian-cross-container #991045193

00:02:31

 
  Containers Layer2
passed alpha-debian-cross-container #991045204

00:02:30

passed amd64-debian-container #991045207

00:03:09

passed amd64-debian-cross-container #991045205

00:02:40

passed amd64-debian-user-cross-container #991045206

00:03:13

passed arm64-debian-cross-container #991045208

00:02:50

passed arm64-test-debian-cross-container #991045210

00:02:34

passed armel-debian-cross-container #991045211

00:02:46

passed armhf-debian-cross-container #991045212

00:02:45

passed hppa-debian-cross-container #991045214

00:02:37

passed m68k-debian-cross-container #991045215

00:02:28

passed mips-debian-cross-container #991045219

00:02:39

passed mips64-debian-cross-container #991045216

00:02:37

passed mips64el-debian-cross-container #991045218

00:02:41

passed mipsel-debian-cross-container #991045220

00:02:41

passed powerpc-debian-cross-container #991045222

00:02:32

passed ppc64-debian-cross-container #991045223

00:02:34

passed ppc64el-debian-cross-container #991045224

00:02:47

passed riscv64-debian-cross-container #991045226

00:02:28

passed s390x-debian-cross-container #991045227

00:02:49

passed sh4-debian-cross-container #991045228

00:02:32

passed sparc64-debian-cross-container #991045230

00:02:36

passed tricore-debian-cross-container #991045231

00:02:40

 
  Build
passed build-clang #991045285

00:46:02

passed build-coroutine-sigaltstack #991045291

00:16:37

passed build-coroutine-ucontext #991045290

00:16:22

passed build-crypto-old-gcrypt #991045293

00:12:13

passed build-crypto-old-nettle #991045292

00:12:19

passed build-crypto-only-gnutls #991045294

00:11:43

passed build-deprecated #991045286

00:13:07

passed build-disabled #991045275

00:28:13

passed build-edk2 #991045234

00:38:36

passed build-libvhost-user #991045305

00:03:28

passed build-opensbi #991045235

00:00:45

passed build-oss-fuzz #991045287

00:49:35

passed build-some-softmmu #991045281

00:21:23

passed build-some-softmmu-plugins #991045284

00:22:23

passed build-system-alpine #991045264

00:36:53

passed build-system-centos #991045272

00:21:00

passed build-system-debian #991045266

00:29:51

passed build-system-fedora #991045270

00:25:58

passed build-system-opensuse #991045274

00:20:12

passed build-system-ubuntu #991045265

00:28:45

passed build-tcg-disabled #991045276

00:20:59

passed build-tci #991045288

00:34:53

passed build-tools-and-docs-debian #991045268

00:09:11

passed build-trace-ftrace-system #991045296

00:15:08

passed build-trace-multi-user #991045295

00:43:01

passed build-trace-ust-system #991045297

00:21:51

passed build-user #991045278

00:39:58

passed build-user-plugins #991045282

00:40:03

passed build-user-static #991045279

00:38:55

passed build-without-default-devices #991045298

00:47:24

passed build-without-default-features #991045300

00:56:03

passed check-dco #991045304

00:01:10

passed check-patch #991045302

00:01:04

passed cross-amd64-xen-only #991045261

00:14:49

passed cross-arm64-system #991045240

00:53:09

passed cross-arm64-user #991045242

00:43:25

passed cross-arm64-xen-only #991045263

00:18:23

passed cross-armel-system #991045236

00:51:51

passed cross-armel-user #991045237

00:43:22

passed cross-armhf-system #991045238

00:47:14

passed cross-armhf-user #991045239

00:42:53

passed cross-i386-system #991045243

00:51:27

passed cross-i386-user #991045244

00:42:31

passed cross-mips-system #991045245

00:49:38

passed cross-mips-user #991045246

00:44:39

passed cross-mips64el-system #991045250

00:51:10

passed cross-mips64el-user #991045251

00:43:33

passed cross-mipsel-system #991045247

00:53:38

passed cross-mipsel-user #991045248

00:48:30

passed cross-ppc64el-system #991045252

00:50:54

passed cross-ppc64el-user #991045254

00:44:15

passed cross-s390x-kvm-only #991045258

00:11:04

passed cross-s390x-system #991045255

00:47:21

passed cross-s390x-user #991045256

00:41:20

passed cross-win32-system #991045259

00:50:53

passed cross-win64-system #991045260

01:05:08

 
  Test
passed acceptance-system-alpine #991045308

00:04:02

passed acceptance-system-centos #991045319

00:04:35

passed acceptance-system-debian #991045314

00:07:42

passed acceptance-system-fedora #991045317

00:08:04

passed acceptance-system-opensuse #991045321

00:04:19

passed acceptance-system-ubuntu #991045311

00:04:56

passed check-crypto-old-gcrypt #991045327

00:17:00

passed check-crypto-old-nettle #991045325

00:16:49

passed check-crypto-only-gnutls #991045328

00:17:00

passed check-deprecated #991045323

00:03:19

passed check-system-alpine #991045307

00:42:40

passed check-system-centos #991045318

00:27:47

passed check-system-debian #991045312

00:42:49

passed check-system-fedora #991045316

00:32:54

passed check-system-opensuse #991045320

00:31:28

passed check-system-ubuntu #991045309

00:38:52

passed pages #991045330

00:09:20

 
  Deploy
passed pages:deploy

00:13:49