ASoC: davinci-mcasp: Fix bit clock polarity settings

IB_NF, NB_IF and IB_IF configured the bc polarity incorrectly. The receive
polarity was set to the same edge as the TX in these cases.

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