[POWERPC] spufs: Fix pointer reference in find_victim

If victim (not ctx) is in spu_run, add victim to rq.

Signed-off-by: Luke Browning <lukebrowning@us.ibm.com>
Acked-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Paul Mackerras <paulus@samba.org>