s390/cpum_sf: remove unnecessary debug statement

Remove debug_sprint_event() statement right after an pr_err()
statement. No additional debug information is generated.
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>