PM / devfreq: passive: fix compiler warning

The recent commit of
PM / devfreq: passive: Use non-devm notifiers
had incurred compiler warning, "unused variable 'dev'".
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>

drivers/devfreq/governor_passive.c

@@ -149,7 +149,6 @@ static int devfreq_passive_notifier_call(struct notifier_block *nb,
 static int devfreq_passive_event_handler(struct devfreq *devfreq,
 				unsigned int event, void *data)
 {
-	struct device *dev = devfreq->dev.parent;
 	struct devfreq_passive_data *p_data
 			= (struct devfreq_passive_data *)devfreq->data;
 	struct devfreq *parent = (struct devfreq *)p_data->parent;