[media] cx24120: do not allow an invalid delivery system types

cx24120_set_frontend currently allows invalid delivery system types
other than SYS_DVBS2 and SYS_DVBS.  Fix this by returning -EINVAL
for invalid values.
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Jemma Denson <jdenson@gmail.com>

drivers/media/dvb-frontends/cx24120.c

@@ -1154,8 +1154,7 @@ static int cx24120_set_frontend(struct dvb_frontend *fe)
 		dev_dbg(&state->i2c->dev,
 			"delivery system(%d) not supported\n",
 			c->delivery_system);
-		ret = -EINVAL;
-		break;
+		return -EINVAL;
 	}
 
 	state->dnxt.delsys = c->delivery_system;