backlight: fix class_find_device() arguments

Michał's previous patch missed this backlight check to fix up the
class_find_device() arguments.
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Cc: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/video/backlight/backlight.c

@@ -371,7 +371,7 @@ void backlight_device_unregister(struct backlight_device *bd)
 EXPORT_SYMBOL(backlight_device_unregister);
 
 #ifdef CONFIG_OF
-static int of_parent_match(struct device *dev, void *data)
+static int of_parent_match(struct device *dev, const void *data)
 {
 	return dev->parent && dev->parent->of_node == data;
 }