s390/perf: fix problem state detection

The P sample bit indicates problem state and not PER.

Fixes: commit a7525982 ("s390: rename struct psw_bits members")
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>