s390x: sclp: Add CPU entry offset comment

Let's make it clear that there is something at the end of the
struct. The exact offset is reported by the cpu_offset member.

Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
9 jobs for sie in 4 minutes and 53 seconds (queued for 2 seconds)
Status Name Job ID Coverage
  Test
passed build-aarch64 #957808292

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passed build-arm #957808295

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passed build-centos7 #957808307

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passed build-clang #957808305

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passed build-i386 #957808304

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passed build-ppc64be #957808297

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passed build-ppc64le #957808299

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passed build-s390x #957808301

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passed build-x86_64 #957808302

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