led: triggers: Fix dereferencing of null pointer

Error was detected by PVS-Studio:
V522 Dereferencing of the null pointer 'led_cdev->trigger' might take place.

Fixes: 2282e125 ("leds: triggers: let struct led_trigger::activate() return an error code")
Signed-off-by: Oleh Kravchenko <oleg@kaa.org.ua>
Reviewed-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>

drivers/leds/led-triggers.c

@@ -167,11 +167,11 @@ int led_trigger_set(struct led_classdev *led_cdev, struct led_trigger *trig)
 		trig->deactivate(led_cdev);
 err_activate:
 
-	led_cdev->trigger = NULL;
-	led_cdev->trigger_data = NULL;
 	write_lock_irqsave(&led_cdev->trigger->leddev_list_lock, flags);
 	list_del(&led_cdev->trig_list);
 	write_unlock_irqrestore(&led_cdev->trigger->leddev_list_lock, flags);
+	led_cdev->trigger = NULL;
+	led_cdev->trigger_data = NULL;
 	led_set_brightness(led_cdev, LED_OFF);
 	kfree(event);