stmmac: dwmac-loongson: fix invalid mdio_node

In current code "plat->mdio_node" is always NULL, the mdio
support is lost as there is no "mdio_bus_data". The original
driver could work as the "mdio" variable is never set to
false, which is described in commit <b0e03950> ("stmmac:
dwmac-loongson: fix uninitialized variable ......"). And
after this commit merged, the "mdio" variable is always
false, causing the mdio supoort logic lost.

Fixes: 30bba69d ("stmmac: pci: Add dwmac support for Loongson")
Signed-off-by: Liu Peibao <liupeibao@loongson.cn>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/20221101060218.16453-1-liupeibao@loongson.cnSigned-off-by: Jakub Kicinski <kuba@kernel.org>

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

@@ -51,7 +51,6 @@ static int loongson_dwmac_probe(struct pci_dev *pdev, const struct pci_device_id
 	struct stmmac_resources res;
 	struct device_node *np;
 	int ret, i, phy_mode;
-	bool mdio = false;
 
 	np = dev_of_node(&pdev->dev);
 
@@ -69,12 +68,10 @@ 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_err(&pdev->dev, "Found MDIO subnode\n");
-		mdio = true;
-	}
+		dev_info(&pdev->dev, "Found MDIO subnode\n");
 
-	if (mdio) {
 		plat->mdio_bus_data = devm_kzalloc(&pdev->dev,
 						   sizeof(*plat->mdio_bus_data),
 						   GFP_KERNEL);