ASoC: rsnd: remove SSI dependent DMAEngine callback

Renesas Gen2 sound will use 2 DMAC
which are Audio-DMAC, and Audio-DMAC-peri-peri.
Current driver has callback function for each DMAC,
because it assumed each DMAC needs special settings.
But it became clear that these can share settings.
This patch removes unnecessary callback

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