PM / Hibernate: hibernation_ops->leave should be checked too

Because hibernate calls hibernation_ops->leave() without checking
whether hibernation_ops->leave is NULL or not, hiberantion_set_ops
should WARN_ON if hibernation_ops->leave is NULL.

This patch added one more condition to check hibernation_ops->leave.

Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>