ARM: dts: mmp2-olpc-xo-1-75: Use symbolic names for audio clocks

These are slighly easier to read.

Signed-off-by: Lubomir Rintel <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]'
Signed-off-by: Arnd Bergmann <[e-mail]>

arch/arm/boot/dts/mmp2-olpc-xo-1-75.dts

···
 /*
  * OLPC XO 1.75 Laptop.
  *
- * Copyright (C) 2018,2019 Lubomir Rintel <[e-mail]>
+ * Copyright (C) 2018,2019,2020 Lubomir Rintel <[e-mail]>
  */
 
 /dts-v1/;
···
 #include <dt-bindings/gpio/gpio.h>
 #include <dt-bindings/input/linux-event-codes.h>
 #include <dt-bindings/interrupt-controller/irq.h>
+#include <dt-bindings/clock/marvell,mmp2-audio.h>
 
 / {
 	model = "OLPC XO-1.75";
···
 		port {
 			rt5631_0: endpoint {
 				mclk-fs = <256>;
-				clocks = <&audio_clk 0>;
+				clocks = <&audio_clk MMP2_CLK_AUDIO_SYSCLK>;
 				remote-endpoint = <&sspa0_0>;
 			};
 		};