[CELL] spufs: use find_first_bit() instead of sched_find_first_bit()

spu_sched->bitmap has MAX_PRIO(=140) width in bits.However, since
ff80a77f

, sched_find_first_bit()
only supports 100-bit bitmaps.

Thus, spu_sched->bitmap should be treated by generic find_first_bit().

Signed-off-by: Masato Noguchi <Masato.Noguchi@jp.sony.com>
Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
Signed-off-by: Arnd Bergmann <arnd.bergmann@de.ibm.com>