powerpc: Use sys_pause for 32-bit pause entry point

sys32_pause is a useless copy of the generic sys_pause.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>