Input: kxtj9 - fix locking typo in kxtj9_set_poll()

According to the comments we want to call mutex_lock() here instead
of mutex_unlock().  That makes more sense.
Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

drivers/input/misc/kxtj9.c

@@ -362,7 +362,7 @@ static ssize_t kxtj9_set_poll(struct device *dev, struct device_attribute *attr,
 		return error;
 
 	/* Lock the device to prevent races with open/close (and itself) */
-	mutex_unlock(&input_dev->mutex);
+	mutex_lock(&input_dev->mutex);
 
 	disable_irq(client->irq);