s390/uaccess: rename tmp1 and tmp2 variables

Rename tmp1 and tmp2 variables to more meaningful val (for value) and rem
(for remainder).

Except for debug sections the output of "objdump -Dr" of the uaccess object
file is identical before/after this change.

Reviewed-by: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>