rcu: Make __call_srcu static

Because __call_srcu() is not used outside kernel/rcu/srcutree.c,
this commit makes it static.
Signed-off-by: Jiang Biao <benbjiang@tencent.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>

kernel/rcu/srcutree.c

@@ -831,8 +831,8 @@ static void srcu_leak_callback(struct rcu_head *rhp)
  * srcu_read_lock(), and srcu_read_unlock() that are all passed the same
  * srcu_struct structure.
  */
-void __call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
-		 rcu_callback_t func, bool do_norm)
+static void __call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
+			rcu_callback_t func, bool do_norm)
 {
 	unsigned long flags;
 	int idx;