locktorture: Make function torture_percpu_rwsem_init() static

The sparse tool complains as follows:

kernel/locking/locktorture.c:569:6: warning:
 symbol 'torture_percpu_rwsem_init' was not declared. Should it be static?

And this function is not used outside of locktorture.c,
so this commit marks it static.
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

kernel/locking/locktorture.c

@@ -566,7 +566,7 @@ static struct lock_torture_ops rwsem_lock_ops = {
 #include <linux/percpu-rwsem.h>
 static struct percpu_rw_semaphore pcpu_rwsem;
 
-void torture_percpu_rwsem_init(void)
+static void torture_percpu_rwsem_init(void)
 {
 	BUG_ON(percpu_init_rwsem(&pcpu_rwsem));
 }