leds: trigger: Fix error path to not unlock the unlocked mutex

ttyname is allocated before the mutex is taken, so it must not be
unlocked in the error path.

Fixes: fd4a641a ("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/20210219133307.4840-2-u.kleine-koenig@pengutronix.deSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/leds/trigger/ledtrig-tty.c

@@ -51,10 +51,8 @@ static ssize_t ttyname_store(struct device *dev,
 
 	if (size) {
 		ttyname = kmemdup_nul(buf, size, GFP_KERNEL);
-		if (!ttyname) {
-			ret = -ENOMEM;
-			goto out_unlock;
-		}
+		if (!ttyname)
+			return -ENOMEM;
 	} else {
 		ttyname = NULL;
 	}
@@ -69,7 +67,6 @@ static ssize_t ttyname_store(struct device *dev,
 
 	trigger_data->ttyname = ttyname;
 
-out_unlock:
 	mutex_unlock(&trigger_data->mutex);
 
 	if (ttyname && !running)