stmmac: dwmac-loongson:Fix missing return value

Add the return value when phy_mode < 0.
Signed-off-by: Nzhaoxiao <long870912@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

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

@@ -109,8 +109,10 @@ static int loongson_dwmac_probe(struct pci_dev *pdev, const struct pci_device_id
 		plat->bus_id = pci_dev_id(pdev);
 
 	phy_mode = device_get_phy_mode(&pdev->dev);
-	if (phy_mode < 0)
+	if (phy_mode < 0) {
 		dev_err(&pdev->dev, "phy_mode not found\n");
+		return phy_mode;
+	}
 
 	plat->phy_interface = phy_mode;
 	plat->interface = PHY_INTERFACE_MODE_GMII;