ARM: dts: ls1021a: add #power-domain-cells for power-controller node

Add the #power-domain-cells for power-controller node as required by the
schema.

Signed-off-by: Li Yang <[e-mail]>
Signed-off-by: Shawn Guo <[e-mail]>

arch/arm/boot/dts/ls1021a.dtsi

···
 			compatible = "fsl,ls1021a-rcpm", "fsl,qoriq-rcpm-2.1+";
 			reg = <0x0 0x1ee2140 0x0 0x8>;
 			#fsl,rcpm-wakeup-cells = <2>;
+			#power-domain-cells = <0>;
 		};
 
 		ftm_alarm0: timer0@29d0000 {