net: ethernet: mediatek: fix error handling inside mtk_mdio_init

Return -ENODEV if the MDIO bus is disabled in the device tree.

Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Acked-by: John Crispin <john@phrozen.org>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.c b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
index 0367f51..d919915 100644
--- a/drivers/net/ethernet/mediatek/mtk_eth_soc.c
+++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
@@ -304,7 +304,7 @@
 	}
 
 	if (!of_device_is_available(mii_np)) {
-		ret = 0;
+		ret = -ENODEV;
 		goto err_put_node;
 	}