uImage.gz is not a target for malta_kvm_guest_defconfig

via, it's a little hard to spot do to the unrelated warnings to fix upstream but:

make --silent --keep-going --jobs=8 O=/home/tuxbuild/.cache/tuxmake/builds/2/tmp ARCH=mips CROSS_COMPILE=mips-linux-gnu- 'HOSTCC=sccache clang' 'CC=sccache clang' uImage.gz
...
make[1]: *** No rule to make target 'uImage.gz'.

So it looks like uImage.gz in not the image name, at least for malta_kvm_guest_defconfig, in which case, we'd boot vmlinux directly in QEMU. So we'd want vmlinux as the build artifact.