PM / devfreq: event: Add const keyword for devfreq_event_ops structure

This patch adds the const keyword for devfreq_event_ops structure
because the ops of devfreq_event_desc structure should not be changed
after initialization.

Cc: Myungjoo Ham <myungjoo.ham@samsung.com>
Cc: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>
diff --git a/include/linux/devfreq-event.h b/include/linux/devfreq-event.h
index 602fbbf..0a83a1e 100644
--- a/include/linux/devfreq-event.h
+++ b/include/linux/devfreq-event.h
@@ -91,7 +91,7 @@
 	const char *name;
 	void *driver_data;
 
-	struct devfreq_event_ops *ops;
+	const struct devfreq_event_ops *ops;
 };
 
 #if defined(CONFIG_PM_DEVFREQ_EVENT)