ASoC: rsnd: remove rsnd_dma::dir

DMAEngine direction can be calculated from rsnd_dai_stream,
So, rsnd_dma::dir does not make sense now.
Let's remove it.

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