locking/static_keys: Fix non static symbol Sparse warning

Fix the following sparse warnings:

  kernel/jump_label.c:473:23: warning:
   symbol 'jump_label_module_nb' was not declared. Should it be static?
Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1466183980-8903-1-git-send-email-weiyj_lk@163.comSigned-off-by: Ingo Molnar <mingo@kernel.org>

kernel/jump_label.c

@@ -422,7 +422,7 @@ jump_label_module_notify(struct notifier_block *self, unsigned long val,
 	return notifier_from_errno(ret);
 }
 
-struct notifier_block jump_label_module_nb = {
+static struct notifier_block jump_label_module_nb = {
 	.notifier_call = jump_label_module_notify,
 	.priority = 1, /* higher than tracepoints */
 };