bmips: shg2500: add missing led controller cells

Fixes the following DT warnings:
../dts/bcm63168-sercomm-shg2500.dts:76.4-14: Warning (reg_format): /ubus/spi@10001000/led-controller@1/led@1:reg: property has invalid length (4 bytes) (#address-cells == 2, #size-cells == 1)
../dts/bcm63168-sercomm-shg2500.dts:75.9-78.5: Warning (avoid_default_addr_size): /ubus/spi@10001000/led-controller@1/led@1: Relying on default #address-cells value
../dts/bcm63168-sercomm-shg2500.dts:75.9-78.5: Warning (avoid_default_addr_size): /ubus/spi@10001000/led-controller@1/led@1: Relying on default #size-cells value

Signed-off-by: Álvaro Fernández Rojas <[email protected]>
(cherry picked from commit fbe0bd5f6453a61fab871bee56883afc5c6308cf)

target/linux/bmips/dts/bcm63168-sercomm-shg2500.dts

@@ -68,6 +68,8 @@
 	status = "okay";
 
 	led-controller@1 {
+		#address-cells = <1>;
+		#size-cells = <0>;
 		compatible = "sercomm,msp430-leds";
 		reg = <1>;
 		spi-max-frequency = <500000>;