ramips: fix ZyXEL Keenetic Viva switch config

The rtl8367b driver never supported a mdio property and it is quite
likely that the switch never worked for the board.

Use the mii-bus property instead to manage the switch via a mdio bus.

Signed-off-by: Franz Flasch <franz.flasch@gmx.at>

target/linux/ramips/dts/kng_rc.dts

@@ -78,7 +78,7 @@
 		compatible = "realtek,rtl8367b";
 		cpu_port = <7>;
 		realtek,extif2 = <1 0 1 1 1 1 1 1 2>;
-		mdio = <&mdio0>;
+		mii-bus = <&mdio0>;
 	};
 };