block/ps3vram: Fix sparse warnings

Fix sparse warnings like these:

 drivers/block/ps3vram.c: warning: incorrect type in assignment (different address spaces)
 drivers/block/ps3vram.c:    expected unsigned int [usertype] *ctrl
 drivers/block/ps3vram.c:    got void [noderef] <asn:2>*

Cc: Jim Paris <jim@jtan.com>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Geoff Levand <geoff@infradead.org>
Acked-by: Jim Paris <jim@jtan.com>
Signed-off-by: Jens Axboe <axboe@fb.com>