ASoC: omap-mcbsp: Clean up dma_data addr initialization code

Make the omap_mcbsp_dma_reg_params() a bit more intuitive to read for the
first glance by using SNDRV_PCM_STREAM_PLAYBACK/CAPTURE and to group the
outermost if case by stream direction.

While there, fix the outdated comment for the function.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Acked-by: Jarkko Nikula <jarkko.nikula@bitmer.com>
Tested-by: Jarkko Nikula <jarkko.nikula@bitmer.com>
Signed-off-by: Mark Brown <broonie@kernel.org>