s390/cpum_cf: log bad return code of function cfset_all_copy

When function cfset_all_copy() fails, also log the bad return code
in the debug statement (when turned on).
No functional change

Signed-off-by: Thomas Richter <tmricht@linux.ibm.com>
Acked-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>