ASoC: rsnd: use rsnd_mod_init() for ADG

Current ADG doesn't use rsnd_mod_init(), but this limitation is no
longer necessary. Let's use common rsnd_mod_init()

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