ftrace: fix check for return value of register_module_notifier in event_trace_init

register_module_notifier() returns zero in the success case.
So fix the inverted fail case check in trace events modules
handler.

[ Impact: fix spurious warning on ftrace initialization]
Reported-by: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: Ming Lei <tom.leiming@gmail.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>

kernel/trace/trace_events.c

@@ -1174,7 +1174,7 @@ static __init int event_trace_init(void)
 	}
 
 	ret = register_module_notifier(&trace_module_nb);
-	if (!ret)
+	if (ret)
 		pr_warning("Failed to register trace events module notifier\n");
 
 	return 0;