ASoC: rsnd: remove struct rsnd_of_data

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.
Now, platform boot style was removed from driver.
This is cleanup patch, and remove pointless struct rsnd_of_data

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