ASoC: davinci-mcasp: Rename the pointer to davinci dma_params as dma_params

It is quite confusing to name the pointer to davinci_pcm_dma_params as
dma_data. Rename the pointer to avoid confusion.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Mark Brown <broonie@linaro.org>