btrfs: fix delayed ref refcount leak in debug assertion

If the delayed_root is not empty we are increasing the number of
references to a delayed_node without decreasing it, causing a leak.  Fix
by decrementing the delayed_node reference count.

Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Leo Martins <loemra.dev@gmail.com>
Reviewed-by: Qu Wenruo <wqu@suse.com>
[ Remove the changelog from the commit message. ]
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

Author: loemraw

fs/btrfs/delayed-inode.c

@@ -1377,7 +1377,10 @@ static int btrfs_wq_run_delayed_node(struct btrfs_delayed_root *delayed_root,
 
 void btrfs_assert_delayed_root_empty(struct btrfs_fs_info *fs_info)
 {
-	WARN_ON(btrfs_first_delayed_node(fs_info->delayed_root));
+	struct btrfs_delayed_node *node = btrfs_first_delayed_node(fs_info->delayed_root);
+
+	if (WARN_ON(node))
+		refcount_dec(&node->refs);
 }
 
 static bool could_end_wait(struct btrfs_delayed_root *delayed_root, int seq)