ASoC: davinci-mcasp: Restructure the davinci_mcasp_calc_clk_div()

Change the return value to error_pmm instead of the BCLK div and handle the
divider configuration to McASP within the function when the set flag is
true.

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