mips: lantiq: danube: add missing properties to cpu node

This fixes the following warnings:
arch/mips/boot/dts/lantiq/danube_easy50712.dtb: cpus: '#address-cells' is a required property
	from schema $id: http://devicetree.org/schemas/cpus.yaml#
arch/mips/boot/dts/lantiq/danube_easy50712.dtb: cpus: '#size-cells' is a required property
	from schema $id: http://devicetree.org/schemas/cpus.yaml#
arch/mips/boot/dts/lantiq/danube_easy50712.dtb: cpu@0 (mips,mips24Kc): 'reg' is a required property
	from schema $id: http://devicetree.org/schemas/mips/cpus.yaml#

Signed-off-by: Aleksander Jan Bajkowski <olek2@wp.pl>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

Author: abajk

arch/mips/boot/dts/lantiq/danube.dtsi

@@ -5,8 +5,12 @@
 	compatible = "lantiq,xway", "lantiq,danube";
 
 	cpus {
+		#address-cells = <1>;
+		#size-cells = <0>;
+
 		cpu@0 {
 			compatible = "mips,mips24Kc";
+			reg = <0>;
 		};
 	};