block: loop: check error using IS_ERR instead of IS_ERR_OR_NULL in loop_add()

blk_mq_init_queue() will not return NULL pointer to its caller,
so it's better to replace IS_ERR_OR_NULL using IS_ERR in loop_add().

If in the future things change to check NULL pointer inside loop_add(),
we should return -ENOMEM as return code instead of PTR_ERR(NULL).
Signed-off-by: Chengguang Xu <cgxu519@gmx.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/loop.c

@@ -1915,7 +1915,7 @@ static int loop_add(struct loop_device **l, int i)
 		goto out_free_idr;
 
 	lo->lo_queue = blk_mq_init_queue(&lo->tag_set);
-	if (IS_ERR_OR_NULL(lo->lo_queue)) {
+	if (IS_ERR(lo->lo_queue)) {
 		err = PTR_ERR(lo->lo_queue);
 		goto out_cleanup_tags;
 	}