ACPI: don't free non-existent backlight in acpi video module

acpi_video_put_one_device was attempting to remove sysfs entries and
unregister a backlight device without first checking that said backlight
device structure had been created.
Signed-off-by: Keith Packard <keithp@keithp.com>
Acked-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Len Brown <len.brown@intel.com>

drivers/acpi/video.c

@@ -2004,8 +2004,11 @@ static int acpi_video_bus_put_one_device(struct acpi_video_device *device)
 	status = acpi_remove_notify_handler(device->dev->handle,
 					    ACPI_DEVICE_NOTIFY,
 					    acpi_video_device_notify);
+	if (device->backlight) {
 		sysfs_remove_link(&device->backlight->dev.kobj, "device");
 		backlight_device_unregister(device->backlight);
+		device->backlight = NULL;
+	}
 	if (device->cdev) {
 		sysfs_remove_link(&device->dev->dev.kobj,
 				  "thermal_cooling");