[media] rtl28xxu: do not return error for unimplemented fe callback

Use of frontend callback is highly hardware design dependent
and whole callback could be optional in many cases. Returning
error by default when callback is not implemented is stupid.
Signed-off-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/usb/dvb-usb-v2/rtl28xxu.c

@@ -591,7 +591,6 @@ static int rtl2832u_fc0012_tuner_callback(struct dvb_usb_device *d,
 		goto err;
 	}
 	return 0;
-
 err:
 	dev_dbg(&d->udev->dev, "%s: failed=%d\n", __func__, ret);
 	return ret;
@@ -643,7 +642,6 @@ static int rtl2832u_tua9001_tuner_callback(struct dvb_usb_device *d,
 	}
 
 	return 0;
-
 err:
 	dev_dbg(&d->udev->dev, "%s: failed=%d\n", __func__, ret);
 	return ret;
@@ -656,17 +654,15 @@ static int rtl2832u_tuner_callback(struct dvb_usb_device *d, int cmd, int arg)
 	switch (priv->tuner) {
 	case TUNER_RTL2832_FC0012:
 		return rtl2832u_fc0012_tuner_callback(d, cmd, arg);
-
 	case TUNER_RTL2832_FC0013:
 		return rtl2832u_fc0013_tuner_callback(d, cmd, arg);
-
 	case TUNER_RTL2832_TUA9001:
 		return rtl2832u_tua9001_tuner_callback(d, cmd, arg);
 	default:
 		break;
 	}
 
-	return -ENODEV;
+	return 0;
 }
 
 static int rtl2832u_frontend_callback(void *adapter_priv, int component,
@@ -682,7 +678,7 @@ static int rtl2832u_frontend_callback(void *adapter_priv, int component,
 		break;
 	}
 
-	return -EINVAL;
+	return 0;
 }
 
 static int rtl2832u_frontend_attach(struct dvb_usb_adapter *adap)