lantiq: change phy-mode to mii for FRITZ!Box 7412

FRITZ!Box 7412 loads the firmware for fast ethernet PHY and mii is
more accurate in this case.
Gmii is used by Gigabit ethernet PHYs.

Signed-off-by: Aleksander Jan Bajkowski <A.Bajkowski@stud.elka.pw.edu.pl>
Reviewed-by: Mathias Kresin <dev@kresin.me>
[minor commit title/message adjustments]
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>

target/linux/lantiq/files/arch/mips/boot/dts/lantiq/vr9_avm_fritz7412.dts

@@ -195,7 +195,7 @@
 		ethernet@2 {
 			compatible = "lantiq,xrx200-pdi-port";
 			reg = <2>;
-			phy-mode = "gmii";
+			phy-mode = "mii";
 			phy-handle = <&phy11>;
 		};
 	};