Btrfs: balance_dirty_pages_ratelimited is causing problems, use nr == 1 always

Signed-off-by: NChris Mason <chris.mason@oracle.com>

fs/btrfs/disk-io.c

@@ -768,7 +768,7 @@ void btrfs_mark_buffer_dirty(struct extent_buffer *buf)
 void btrfs_btree_balance_dirty(struct btrfs_root *root, unsigned long nr)
 {
 	balance_dirty_pages_ratelimited_nr(
-			root->fs_info->btree_inode->i_mapping, nr);
+			root->fs_info->btree_inode->i_mapping, 1);
 }
 
 void btrfs_set_buffer_defrag(struct extent_buffer *buf)