Otherwise the request-based DM blk-mq request_queue will be put into
service without being properly exported via sysfs.

Cc: stable@vger.kernel.org
Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>