sched/ext: Use tg_cgroup() to elieminate duplicate code

Use tg_cgroup() to eliminate duplicate code patterns
in scx_bpf_task_cgroup().

Signed-off-by: Zhang Qiao <zhangqiao22@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
(cherry picked from commit 161853a78bb2f304eb16f025ea08bd1bbe61516c)

kernel/sched/ext.c

@@ -7170,15 +7170,8 @@ __bpf_kfunc struct cgroup *scx_bpf_task_cgroup(struct task_struct *p)
 	if (!scx_kf_allowed_on_arg_tasks(__SCX_KF_RQ_LOCKED, p))
 		goto out;
 
-	/*
-	 * A task_group may either be a cgroup or an autogroup. In the latter
-	 * case, @tg->css.cgroup is %NULL. A task_group can't become the other
-	 * kind once created.
-	 */
-	if (tg && tg->css.cgroup)
-		cgrp = tg->css.cgroup;
-	else
-		cgrp = &cgrp_dfl_root.cgrp;
+	cgrp = tg_cgrp(tg);
+
 out:
 	cgroup_get(cgrp);
 	return cgrp;