[media] cxd2820r: do not allow get_frontend() when demod is not initialized

This fixes bug introduced by multi-frontend to single-frontend change.

Finally HAS_LOCK is got back!
We are not allowed to access hardware in sleep mode...
Chip did not like when .get_frontend() reads some registers while
chip was sleeping and due to that HAS_LOCK bit was never gained.

TODO: We should add logic for dvb-core to drop out illegal calls like that.
Signed-off-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/dvb/frontends/cxd2820r_core.c

@@ -309,9 +309,14 @@ static int cxd2820r_read_status(struct dvb_frontend *fe, fe_status_t *status)
 
 static int cxd2820r_get_frontend(struct dvb_frontend *fe)
 {
+	struct cxd2820r_priv *priv = fe->demodulator_priv;
 	int ret;
 
 	dbg("%s: delsys=%d", __func__, fe->dtv_property_cache.delivery_system);
+
+	if (priv->delivery_system == SYS_UNDEFINED)
+		return 0;
+
 	switch (fe->dtv_property_cache.delivery_system) {
 	case SYS_DVBT:
 		ret = cxd2820r_get_frontend_t(fe);