ASoC: rsnd: dvc: add rsnd_dvc_of_node()

This patch adds rsnd_dvc_of_node() to get DVC subnode from DT.
This is prepare for new DT bindings for 1st DMAC

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

sound/soc/sh/rcar/dvc.c

@@ -24,6 +24,9 @@ struct rsnd_dvc {
 	struct rsnd_kctrl_cfg_s rdown;	/* Ramp Rate Down */
 };
 
+#define rsnd_dvc_of_node(priv) \
+	of_get_child_by_name(rsnd_priv_to_dev(priv)->of_node, "rcar_sound,dvc")
+
 #define rsnd_mod_to_dvc(_mod)	\
 	container_of((_mod), struct rsnd_dvc, mod)