enetc_mdio: Fix devclass name

Use correct devclass name, due to the mismatch miibus would attach
to the wrong thing causing mii_attach to silently fail.

Fixes: dfcaa2c18b (enetc_mdio: Support building the driver ...)

sys/dev/enetc/enetc_mdio_pci.c

@@ -177,7 +177,7 @@ static device_method_t	enetc_mdio_pci_methods[] ={
 };
 
 static driver_t	enetc_mdio_pci_driver = {
-	"enetc_mdio_pci",
+	"enetc_mdio",
 	enetc_mdio_pci_methods,
 	sizeof(struct enetc_mdio_pci_softc),
 };