dell-laptop: touchpad LED should persist its status after S3

Touchpad LED will not turn on after S3, it will make the touchpad status
doesn't consist with the LED.
By adding one flag to let the LED device restore it's status.
Signed-off-by: NAceLan Kao <acelan.kao@canonical.com>
Signed-off-by: NMatthew Garrett <mjg@redhat.com>

drivers/platform/x86/dell-laptop.c

@@ -641,6 +641,7 @@ static void touchpad_led_set(struct led_classdev *led_cdev,
 static struct led_classdev touchpad_led = {
 	.name = "dell-laptop::touchpad",
 	.brightness_set = touchpad_led_set,
+	.flags = LED_CORE_SUSPENDRESUME,
 };
 
 static int __devinit touchpad_led_init(struct device *dev)