rbd: kill rbd_dev->q

A copy of rbd_dev->disk->queue is held in rbd_dev->q, but it's
never actually used.  So get just get rid of the field.

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index 7726368..774a36b 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -155,7 +155,6 @@
 
 	int			major;		/* blkdev assigned major */
 	struct gendisk		*disk;		/* blkdev's gendisk and rq */
-	struct request_queue	*q;
 
 	struct rbd_options	rbd_opts;
 	struct rbd_client	*rbd_client;
@@ -1923,7 +1922,6 @@
 	q->queuedata = rbd_dev;
 
 	rbd_dev->disk = disk;
-	rbd_dev->q = q;
 
 	/* finally, announce the disk to the world */
 	set_capacity(disk, total_size / SECTOR_SIZE);