ASoC: rsnd: remove platform boot support from core.c

No board is using Renesas sound driver via platform boot now.
This means all user is using DT boot. Platform boot support is
no longer needed. But, it strongly depends on platform boot style.
This patch removes platform boot support from core.c

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

sound/soc/sh/rcar/ssi.c

@@ -88,8 +88,6 @@ struct rsnd_ssi {
 #define rsnd_ssi_mode_flags(p) ((p)->info->flags)
 #define rsnd_ssi_dai_id(ssi) ((ssi)->info->dai_id)
 #define rsnd_ssi_is_parent(ssi, io) ((ssi) == rsnd_io_to_mod_ssip(io))
-#define rsnd_ssi_of_node(priv) \
-	of_get_child_by_name(rsnd_priv_to_dev(priv)->of_node, "rcar_sound,ssi")
 
 int rsnd_ssi_use_busif(struct rsnd_dai_stream *io)
 {