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.

Reported-by: Pavel Machek <pavel@ucw.cz>
Fixes: fd4a641 ("leds: trigger: implement a tty trigger")
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>

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;
 	}