ARM: shmobile: r8a7778: tidyup #sound-dai-cells settings

Renesas sound driver needs #sound-dai-cells settings, but, this usage
is a little bit confusable. It came from ALSA SoC historical reasons.
The sound DAI naming method is different between Single/Multi DAI in
the ALSA framework, and it is used for sound card matching.
And this #sound-dai-cells has relationship to it.
Current SoC dtsi has #sound-dai-cells = <1> as default settings
(= it is assuming that board/platform has multi DAI), and
board/platform side needs to overwrite it if board/platform was single
DAI. This style is more confusable for users.
This patch removes SoC side default settings, and force to set it by
board/platform side.
Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>

arch/arm/boot/dts/r8a7778.dtsi

@@ -236,7 +236,12 @@ tmu2: timer@ffd82000 {
 	};
 
 	rcar_sound: sound@ffd90000 {
-		#sound-dai-cells = <1>;
+		/*
+		 * #sound-dai-cells is required
+		 *
+		 * Single DAI : #sound-dai-cells = <0>;         <&rcar_sound>;
+		 * Multi  DAI : #sound-dai-cells = <1>;         <&rcar_sound N>;
+		 */
 		compatible = "renesas,rcar_sound-r8a7778", "renesas,rcar_sound-gen1";
 		reg =	<0xffd90000 0x1000>,	/* SRU */
 			<0xffd91000 0x240>,	/* SSI */