Documentation/atomic_ops.txt: fix sample code

list_add() lost a parameter in sample code.

Signed-off-by: Figo.zhang <figo1802@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/Documentation/atomic_ops.txt b/Documentation/atomic_ops.txt
index 4ef2450..396bec3 100644
--- a/Documentation/atomic_ops.txt
+++ b/Documentation/atomic_ops.txt
@@ -229,10 +229,10 @@
 counting, and it works such that once the counter falls to zero it can
 be guaranteed that no other entity can be accessing the object:
 
-static void obj_list_add(struct obj *obj)
+static void obj_list_add(struct obj *obj, struct list_head *head)
 {
 	obj->active = 1;
-	list_add(&obj->list);
+	list_add(&obj->list, head);
 }
 
 static void obj_list_del(struct obj *obj)