s390/cpum_sf: handle casts consistently

The casts are written in two different notations:
   (cast) expression
and
   (cast)expression
Convert statements with the first notation to the second notation.
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>