leds: trigger/tty: Use led_set_brightness_sync() from workqueue

led_set_brightness() involves scheduling a workqueue. As here the led's
brightness setting is done in context of the trigger's workqueue this is
unjustified overhead and it's more sensible to use
led_set_brightness_sync().

Fixes: fd4a641ac8 ("leds: trigger: implement a tty trigger")
Reported-by: Pavel Machek <pavel@ucw.cz>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/20210219133307.4840-3-u.kleine-koenig@pengutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/leds/trigger/ledtrig-tty.c

@@ -122,12 +122,12 @@ static void ledtrig_tty_work(struct work_struct *work)
 
 	if (icount.rx != trigger_data->rx ||
 	    icount.tx != trigger_data->tx) {
-		led_set_brightness(trigger_data->led_cdev, LED_ON);
+		led_set_brightness_sync(trigger_data->led_cdev, LED_ON);
 
 		trigger_data->rx = icount.rx;
 		trigger_data->tx = icount.tx;
 	} else {
-		led_set_brightness(trigger_data->led_cdev, LED_OFF);
+		led_set_brightness_sync(trigger_data->led_cdev, LED_OFF);
 	}
 
 out: