Input: tsc2007 - make sure platform provides get_pendown_state()

The platform codes must provide get_pendown_state() for the driver
to work properly.
Signed-off-by: Kwangwoo Lee <kwangwoo.lee@gmail.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

drivers/input/touchscreen/tsc2007.c

@@ -256,7 +256,7 @@ static int tsc2007_probe(struct i2c_client *client,
 	struct input_dev *input_dev;
 	int err;
 
-	if (!pdata) {
+	if (!pdata || !pdata->get_pendown_state) {
 		dev_err(&client->dev, "platform data is required!\n");
 		return -EINVAL;
 	}