ASoC: ep93xx: Open code dma channel request

Currently the ep93xx DMA code is one of the few users relying on the fact
that the compat code uses the dma_data as the filter data for non-DT
channel requests. Since the rest of the core expects this to be a struct
snd_dmaengine_dai_data this isn't terribly helpful this will be changed to
use the already existing filter data so avoid breaking ep93xx by open
coding the current behaviour.

Signed-off-by: Mark Brown <broonie@linaro.org>
Acked-by: Lars-Peter Clausen <lars@metafoo.de>