s390/kvm: Initialize uninitialized flags variable

s390/kvm: Initialize uninitialized flags variable

The flags variable was being used uninitialized.
Initialize it to 0 as expected.

For some reason neither gcc nor clang reported a warning.

Fixes: 05066cafa925 ("s390/mm/fault: Handle guest-related program interrupts in KVM")
Reported-by: Janosch Frank <frankja@linux.ibm.com>
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Link: https://lore.kernel.org/r/20241030161906.85476-1-imbrenda@linux.ibm.com
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>