ARM: shmobile: koelsch: add Volume Ramp usage on comment

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>

arch/arm/boot/dts/r8a7791-koelsch.dts

@@ -27,6 +27,15 @@
  *
  *	amixer set "DVC Out Mute" on
  *	amixer set "DVC In Mute" on
+ *
+ * You can use Volume Ramp
+ *
+ *	amixer set "DVC Out Ramp Up Rate"   "0.125 dB/64 steps"
+ *	amixer set "DVC Out Ramp Down Rate" "0.125 dB/512 steps"
+ *	amixer set "DVC Out Ramp" on
+ *	aplay xxx.wav &
+ *	amixer set "DVC Out"  80%  // Volume Down
+ *	amixer set "DVC Out" 100%  // Volume Up
  */
 
 /dts-v1/;