ASoC: rsnd: save priv in struct rsnd_dai

Current rsnd driver has rsnd_mod_to_priv() macro, and struct rsnd_mod
has struct rsnd_priv pointer. But, it is waste of memory from data
structure point of view.
Today we can link mod <-> io <-> rdai each other, so saving priv in
rdai is very reasonable.

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