ext4: use correct depth value

Inode's depth can be changed from here:
ext4_ext_try_to_merge() ->ext4_ext_try_to_merge_up()
We must use correct value.
Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Jan Kara <jack@suse.cz>

fs/ext4/extents.c

@@ -3254,7 +3254,7 @@ static int ext4_split_extent_at(handle_t *handle,
 
 fix_extent_len:
 	ex->ee_len = orig_ex.ee_len;
-	ext4_ext_dirty(handle, inode, path + depth);
+	ext4_ext_dirty(handle, inode, path + path->p_depth);
 	return err;
 }