s390/cpum_sf: simplify function setup_pmu_cpu

Print the error message when the FAILURE flag is set.
This saves on pr_err statement as the text of the error message
is identical in both failures.
Also observe reverse Xmas tree variable declarations in this function.
No functional change.

Signed-off-by: Thomas Richter <tmricht@linux.ibm.com>
Acked-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>