[S390] s390: use sys_pause for 31bit pause entry point

sys32_pause is a useless copy of the generic sys_pause.
(and it's certainly not there for old sparc32 binaries..)

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>