ASoC: rsnd: clarify scu.c area

scu.c cares SRU(Gen1) / SCU(Gen2) / SSIU(Gen2)
Signed-off-by: NKuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: NMark Brown <broonie@linaro.org>

sound/soc/sh/rcar/scu.c

@@ -40,6 +40,20 @@ struct rsnd_scu {
  *
  */
 
+/*
+ * scu.c is caring...
+ *
+ * Gen1
+ *
+ * [mem] -> [SRU] -> [SSI]
+ *        |--------|
+ *
+ * Gen2
+ *
+ * [mem] -> [SCU] -> [SSIU] -> [SSI]
+ *        |-----------------|
+ */
+
 /*
  *	How to use SRC bypass mode for debugging
  *