stmmac: dwmac-loongson: Make sure MDIO is initialized before use

Generic code will use mdio. If it is not initialized before use,
the kernel will Oops.

Fixes: 30bba69d ("stmmac: pci: Add dwmac support for Loongson")
Signed-off-by: Yanteng Si <siyanteng@loongson.cn>
Signed-off-by: Feiyang Chen <chenfeiyang@loongson.cn>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/stmicro/stmmac/dwmac-loongson.c

@@ -68,17 +68,15 @@ static int loongson_dwmac_probe(struct pci_dev *pdev, const struct pci_device_id
 	if (!plat)
 		return -ENOMEM;
 
-	plat->mdio_node = of_get_child_by_name(np, "mdio");
-	if (plat->mdio_node) {
-		dev_info(&pdev->dev, "Found MDIO subnode\n");
-
 	plat->mdio_bus_data = devm_kzalloc(&pdev->dev,
 					   sizeof(*plat->mdio_bus_data),
 					   GFP_KERNEL);
-		if (!plat->mdio_bus_data) {
-			ret = -ENOMEM;
-			goto err_put_node;
-		}
+	if (!plat->mdio_bus_data)
+		return -ENOMEM;
+
+	plat->mdio_node = of_get_child_by_name(np, "mdio");
+	if (plat->mdio_node) {
+		dev_info(&pdev->dev, "Found MDIO subnode\n");
 		plat->mdio_bus_data->needs_reset = true;
 	}