cgroup/cpuset: Update comment on callback_lock

Since commit 51ffe41178 ("cpuset: convert away from cftype->read()"),
cpuset_common_file_read() has been renamed.

Signed-off-by: Xiu Jianfeng <xiujianfeng@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

kernel/cgroup/cpuset.c

@@ -434,7 +434,7 @@ static struct cpuset top_cpuset = {
  * by other task, we use alloc_lock in the task_struct fields to protect
  * them.
  *
- * The cpuset_common_file_read() handlers only hold callback_lock across
+ * The cpuset_common_seq_show() handlers only hold callback_lock across
  * small pieces of code, such as when reading out possibly multi-word
  * cpumasks and nodemasks.
  *