Btrfs: drop the delalloc_bytes check in shrink_delalloc

Even when delalloc_bytes is zero, we may need to sleep while waiting
for delalloc space.
Signed-off-by: NChris Mason <chris.mason@oracle.com>

fs/btrfs/extent-tree.c

@@ -3314,10 +3314,6 @@ static int shrink_delalloc(struct btrfs_trans_handle *trans,
 	if (reserved == 0)
 		return 0;
 
-	/* nothing to shrink - nothing to reclaim */
-	if (root->fs_info->delalloc_bytes == 0)
-		return 0;
-
 	max_reclaim = min(reserved, to_reclaim);
 
 	while (loops < 1024) {