ARM: dts: r8a7794: add audio clocks

Describe  the external audio clocks (signals AUDIO_CLK[ABC]) required by
the sound driver.  Boards that provide audio clocks need to  override the
clock frequencies.

This patch is based on the commit 0d3dbde84a45 ("ARM: shmobile: r8a7791:
add  audio clock on DTSI").

Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Acked-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>

arch/arm/boot/dts/r8a7794.dtsi

@@ -952,6 +952,27 @@
 			clock-frequency = <0>;
 		};
 
+		/*
+		 * The external audio clocks are configured  as 0 Hz fixed
+		 * frequency clocks by default.  Boards that provide audio
+		 * clocks should override them.
+		 */
+		audio_clka: audio_clka {
+			compatible = "fixed-clock";
+			#clock-cells = <0>;
+			clock-frequency = <0>;
+		};
+		audio_clkb: audio_clkb {
+			compatible = "fixed-clock";
+			#clock-cells = <0>;
+			clock-frequency = <0>;
+		};
+		audio_clkc: audio_clkc {
+			compatible = "fixed-clock";
+			#clock-cells = <0>;
+			clock-frequency = <0>;
+		};
+
 		/* Special CPG clocks */
 		cpg_clocks: cpg_clocks@e6150000 {
 			compatible = "renesas,r8a7794-cpg-clocks",