[media] ts2020: call get_rf_strength from frontend

Restore ds3000.c read_signal_strength.
Call tuner get_rf_strength from frontend read_signal_strength.
We are able to do a NULL check and doesn't limit the tuner
attach to the frontend attach area.
At the moment the lmedm04 tuner attach is stuck in frontend
attach area.

Signed-off-by: Malcolm Priestley <tvboxspy@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
diff --git a/drivers/media/dvb-frontends/m88rs2000.c b/drivers/media/dvb-frontends/m88rs2000.c
index 283c90f..4da5272 100644
--- a/drivers/media/dvb-frontends/m88rs2000.c
+++ b/drivers/media/dvb-frontends/m88rs2000.c
@@ -446,7 +446,9 @@
 static int m88rs2000_read_signal_strength(struct dvb_frontend *fe,
 	u16 *strength)
 {
-	*strength = 0;
+	if (fe->ops.tuner_ops.get_rf_strength)
+		fe->ops.tuner_ops.get_rf_strength(fe, strength);
+
 	return 0;
 }