leds: triggers: let struct led_trigger::activate() return an error code

Given that activating a trigger can fail, let the callback return an
indication. This prevents to have a trigger active according to the
"trigger" sysfs attribute but not functional.

All users are changed accordingly to return 0 for now. There is no intended
change in behaviour.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>

drivers/tty/vt/keyboard.c

@@ -959,7 +959,7 @@ struct kbd_led_trigger {
 	unsigned int mask;
 };
 
-static void kbd_led_trigger_activate(struct led_classdev *cdev)
+static int kbd_led_trigger_activate(struct led_classdev *cdev)
 {
 	struct kbd_led_trigger *trigger =
 		container_of(cdev->trigger, struct kbd_led_trigger, trigger);
@@ -970,6 +970,8 @@ static void kbd_led_trigger_activate(struct led_classdev *cdev)
 				  ledstate & trigger->mask ?
 					LED_FULL : LED_OFF);
 	tasklet_enable(&keyboard_tasklet);
+
+	return 0;
 }
 
 #define KBD_LED_TRIGGER(_led_bit, _name) {			\