ASoC: rsnd: don't use schedule_work() when rsnd_dma_start()

rsnd_dma_start() is the function to start DMAEngine.
Current code is using schedule_work() for it,
but it breaks DMAC/SSI register setting timing.
Don't use schedule_work() on it.

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