s390/perf_cpum_sf: Convert to use try_cmpxchg128()

Convert cmpxchg128() usages to try_cmpxchg128() in order to generate
slightly better code.

Reviewed-by: Juergen Christ <jchrist@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>