ofnode: Update of_add_subnode() to indicate name is alloced

This function allocates memory for the node name, so mention this in the
function comment.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/include/dm/ofnode.h b/include/dm/ofnode.h
index 890f0e6..c5f0a6d 100644
--- a/include/dm/ofnode.h
+++ b/include/dm/ofnode.h
@@ -1809,7 +1809,7 @@
  * of_add_subnode() - add a new subnode to a node
  *
  * @parent:	parent node to add to
- * @name:	name of subnode
+ * @name:	name of subnode (allocated by this function)
  * @nodep:	returns pointer to new subnode (valid if the function returns 0
  *	or -EEXIST)
  * Returns 0 if OK, -EEXIST if already exists, -ENOMEM if out of memory, other