blk-mq: kill q->mq_map

It's just a pointer to set->mq_map, use that instead. Move the
assignment a bit earlier, so we always know it's valid.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

include/linux/blkdev.h

@@ -409,8 +409,6 @@ struct request_queue {
 
 	const struct blk_mq_ops	*mq_ops;
 
-	unsigned int		*mq_map;
-
 	/* sw queues */
 	struct blk_mq_ctx __percpu	*queue_ctx;
 	unsigned int		nr_queues;