Revert "s390/mem_detect: do not update output parameters on failure"

This reverts commit cbc29f10.

Get rid of the following smatch warnings:

arch/s390/include/asm/mem_detect.h:86 get_mem_detect_end() error: uninitialized symbol 'end'.
arch/s390/include/asm/mem_detect.h:86 get_mem_detect_end() error: uninitialized symbol 'end'.
arch/s390/boot/vmem.c:256 setup_vmem() error: uninitialized symbol 'start'.
arch/s390/boot/vmem.c:258 setup_vmem() error: uninitialized symbol 'end'.

Note that there is no bug in the code. This is purely to silence smatch.

Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>