[POWERPC] spufs: bind_context sets SPU_STATE_RUNNABLE

Only bind_context/unbind_context change the spu context state.  Thus
we can move all assignents of SPU_STATE_RUNNABLE into bind_context,
which parallels the unbind side aswell.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Arnd Bergmann <arnd.bergmann@de.ibm.com>