ASoC: imx: initialize dma_params burstsize just in imx-ssi

It's not necessary for imx-pcm-dma-mx2 to access imx_ssi.dma_params
for burstsize initialization.  Instead, it can just be done in imx-ssi
probe function once.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>