PM / Sleep: Replace mutex_[un]lock(&pm_mutex) with [un]lock_system_sleep()

Using [un]lock_system_sleep() is safer than directly using mutex_[un]lock()
on 'pm_mutex', since the latter could lead to freezing failures. Hence convert
all the present users of mutex_[un]lock(&pm_mutex) to use these safe APIs
instead.

Suggested-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Reviewed-by: Simon Horman <horms@verge.net.au>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
diff --git a/kernel/power/suspend.c b/kernel/power/suspend.c
index d336b27..4fd51be 100644
--- a/kernel/power/suspend.c
+++ b/kernel/power/suspend.c
@@ -42,9 +42,9 @@
  */
 void suspend_set_ops(const struct platform_suspend_ops *ops)
 {
-	mutex_lock(&pm_mutex);
+	lock_system_sleep();
 	suspend_ops = ops;
-	mutex_unlock(&pm_mutex);
+	unlock_system_sleep();
 }
 EXPORT_SYMBOL_GPL(suspend_set_ops);