hwmon: (max6650) Fix lock imbalance

Add omitted update_lock to one switch/case in set_div.
Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Acked-by: Hans J. Koch <hjk@linutronix.de>
Signed-off-by: Jean Delvare <khali@linux-fr.org>

drivers/hwmon/max6650.c

@@ -418,6 +418,7 @@ static ssize_t set_div(struct device *dev, struct device_attribute *devattr,
 		data->count = 3;
 		break;
 	default:
+		mutex_unlock(&data->update_lock);
 		dev_err(&client->dev,
 			"illegal value for fan divider (%d)\n", div);
 		return -EINVAL;