ASoC: rcar: tidyup simple-card example for CPU node

commit a5702e1cb3c ("ASoC: rsnd: Drop unit-addresses without reg
properties") modifies simple-card multi CPU nodes.
But, naming of "cpu-x" breaks probing.
Let's add reg = <x>; instead of renaming node.

Reported-by: Hiroyuki Yokoyama <hiroyuki.yokoyama.vx@renesas.com>
CC: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/renesas,rsnd.txt

@@ -197,12 +197,17 @@ Ex)
 	[MEM] -> [SRC2] -> [CTU03] -+
 
 	sound {
+		#address-cells = <1>;
+		#size-cells = <0>;
+
 		compatible = "simple-scu-audio-card";
 		...
-		simple-audio-card,cpu-0 {
+		simple-audio-card,cpu@0 {
+			reg = <0>;
 			sound-dai = <&rcar_sound 0>;
 		};
-		simple-audio-card,cpu-1 {
+		simple-audio-card,cpu@1 {
+			reg = <1>;
 			sound-dai = <&rcar_sound 1>;
 		};
 		simple-audio-card,codec {