block: move blk_exit_queue into __blk_release_queue

Commit 498f6650 ("block: Fix a race between the cgroup code and
request queue initialization") moves what blk_exit_queue does into
blk_cleanup_queue() for fixing issue caused by changing back
queue lock.

However, after legacy request IO path is killed, driver queue lock
won't be used at all, and there isn't story for changing back
queue lock. Then the issue addressed by Commit 498f6650 doesn't
exist any more.

So move move blk_exit_queue into __blk_release_queue.

This patch basically reverts the following two commits:

	498f6650 block: Fix a race between the cgroup code and request queue initialization
	24ecc358

 block: Ensure that a request queue is dissociated from the cgroup controller

Cc: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>