cgroup: cls: remove unnecessary task_cls_classid

We can get classid through cgroup_subsys_state,
this is directviewing and effective.
Signed-off-by: Gao feng <gaofeng@cn.fujitsu.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/cls_cgroup.c

@@ -72,11 +72,11 @@ static void cgrp_attach(struct cgroup_subsys_state *css,
 			struct cgroup_taskset *tset)
 {
 	struct task_struct *p;
-	void *v;
+	struct cgroup_cls_state *cs = css_cls_state(css);
+	void *v = (void *)(unsigned long)cs->classid;
 
 	cgroup_taskset_for_each(p, css, tset) {
 		task_lock(p);
-		v = (void *)(unsigned long)task_cls_classid(p);
 		iterate_fd(p->files, 0, update_classid, v);
 		task_unlock(p);
 	}