block: drop device references in bsg_queue_rq()

Make sure that bsg_queue_rq() calls put_device() if an error is
encountered after get_device() was successful.

Fixes: cd2f076f ("bsg: convert to use blk-mq")
Signed-off-by: Martin Wilck <mwilck@suse.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>