dm thin: remove needless request_queue NULL pointer check

Since commit ff9ea323 ("block, bdi: an active gendisk always has a
request_queue associated with it") the request_queue pointer returned
from bdev_get_queue() shall never be NULL.
Signed-off-by: Xu Wang <vulab@iscas.ac.cn>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm-thin.c

@@ -2816,7 +2816,7 @@ static bool data_dev_supports_discard(struct pool_c *pt)
 {
 	struct request_queue *q = bdev_get_queue(pt->data_dev->bdev);
 
-	return q && blk_queue_discard(q);
+	return blk_queue_discard(q);
 }
 
 static bool is_factor(sector_t block_size, uint32_t n)