ASoC: davinci-mcasp: Update MCASP_VERSION_4 platform driver registration

Version 4 of McASP is using omap-pcm as platform driver and the omap-pcm
platform need to be registered using the cpu dai's device.

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