s390/mem_detect: rely on diag260() if sclp_early_get_memsize() fails

s390/mem_detect: rely on diag260() if sclp_early_get_memsize() fails

[ Upstream commit eb33f9eb304a4c18beb5ba6362eaa5c4beaf40d8 ]

In case sclp_early_get_memsize() fails but diag260() succeeds make sure
some sane value is returned. This error scenario is highly unlikely,
but this change makes system able to boot in such case.

Suggested-by: Alexander Gordeev <agordeev@linux.ibm.com>
Reviewed-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Stable-dep-of: 22476f47b6b7 ("s390/boot: fix mem_detect extended area allocation")
Signed-off-by: Sasha Levin <sashal@kernel.org>