[POWERPC] spufs: fix typos in sched.c comments

Fix a few typos in the spufs scheduler comments

Signed-off-by: Julio M. Merino Vidal <jmerino@ac.upc.edu>
Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>