cpuset: fix non static symbol warning

Fixes the following sparse warning:

kernel/cpuset.c:2088:6: warning:
 symbol 'cpuset_fork' was not declared. Should it be static?

Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index c08585a..2b4c20a 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -2085,7 +2085,7 @@
  * which could have been changed by cpuset just after it inherits the
  * state from the parent and before it sits on the cgroup's task list.
  */
-void cpuset_fork(struct task_struct *task)
+static void cpuset_fork(struct task_struct *task)
 {
 	if (task_css_is_root(task, cpuset_cgrp_id))
 		return;