ASoC: audio-graph-scu-card: tidyup "convert-rate/channels" parsing on Doc

audio-graph-scu-card.c is supporting "convert-rate/channels" which is
used for DPCM.
But, sound card might have multi codecs, and each codec might need
each convert-rate/channels.

This patch supports each codec's convert-rate/channles support.
top node convert-rate/channels will overwrite settings if exist.

It can't support each codec's convert-rate/channels if sound card had
multi codecs without this patch.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/audio-graph-scu-card.txt

@@ -80,7 +80,6 @@ Example 2. 2 CPU 1 Codec (Mixing)
 		routing = "codec Playback", "DAI0 Playback",
 			  "codec Playback", "DAI1 Playback",
 			  "DAI0 Capture",   "codec Capture";
-		convert-rate = <48000>;
 
 		dais = <&cpu_port0
 			&cpu_port1>;
@@ -90,6 +89,7 @@ Example 2. 2 CPU 1 Codec (Mixing)
 		...
 
 		audio-graph-card,prefix = "codec";
+		audio-graph-card,convert-rate = <48000>;
 		port {
 			codec_endpoint0: endpoint {
 				remote-endpoint = <&cpu_endpoint0>;