ARM: shmobile: r8a7791 dtsi: Drop "renesas,rcar_sound" compatible value

The "renesas,rcar_sound" compatible property value was never processed
nor documented.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>

arch/arm/boot/dts/r8a7791.dtsi

@@ -1382,7 +1382,7 @@ pciec: pcie@fe000000 {
 
 	rcar_sound: rcar_sound@ec500000 {
 		#sound-dai-cells = <1>;
-		compatible =  "renesas,rcar_sound-r8a7791", "renesas,rcar_sound-gen2", "renesas,rcar_sound";
+		compatible =  "renesas,rcar_sound-r8a7791", "renesas,rcar_sound-gen2";
 		reg =	<0 0xec500000 0 0x1000>, /* SCU */
 			<0 0xec5a0000 0 0x100>,  /* ADG */
 			<0 0xec540000 0 0x1000>, /* SSIU */