simplify augment walk after insert

Author: epsilon-0

include/tree.h

@@ -330,10 +330,8 @@ name##_RB_INSERT_FINISH(struct name *head, struct type *parent,		\
 	else {								\
 		_RB_SET_CHILD(parent, insdir, elm, field);		\
 		tmp = name##_RB_INSERT_BALANCE(head, parent, elm);	\
-		_RB_GET_PARENT(tmp, parent, field);			\
 	}								\
-	(void)_RB_AUGMENT(tmp);						\
-	_RB_AUGMENT_WALK(head, parent, field);				\
+	_RB_AUGMENT_WALK(head, tmp, field);				\
 	return (NULL);							\
 }									\
 									\