UBIFS: fix commentary

Znode may refer both data nodes and indexing nodes
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>

fs/ubifs/ubifs.h

@@ -707,8 +707,8 @@ struct ubifs_jhead {
  * struct ubifs_zbranch - key/coordinate/length branch stored in znodes.
  * @key: key
  * @znode: znode address in memory
- * @lnum: LEB number of the indexing node
- * @offs: offset of the indexing node within @lnum
+ * @lnum: LEB number of the target node (indexing node or data node)
+ * @offs: target node offset within @lnum
  * @len: target node length
  */
 struct ubifs_zbranch {