btrfs: uuid-tree: remove unnecessary call to btrfs_mark_buffer_dirty()

The call to btrfs_mark_buffer_dirty() at btrfs_uuid_tree_add() is not
necessary as we have a path setup for writing with btrfs_search_slot()
having a 'cow' argument set to 1 (through btrfs_insert_empty_item()).

This just makes the code more verbose, confusing and add a little extra
overhead and well as increase the module's text size, so remove it.

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/uuid-tree.c

@@ -140,8 +140,6 @@ int btrfs_uuid_tree_add(struct btrfs_trans_handle *trans, const u8 *uuid, u8 typ
 	ret = 0;
 	subid_le = cpu_to_le64(subid_cpu);
 	write_extent_buffer(eb, &subid_le, offset, sizeof(subid_le));
-	btrfs_mark_buffer_dirty(trans, eb);
-
 out:
 	btrfs_free_path(path);
 	return ret;