ASoC: davinci-mcasp: Be consistent with the use of base in davinci_mcasp_set_dai_fmt

Replace mcasp->base use with plain base in the davinci_mcasp_set_dai_fmt()
function since it has been already used by the remaining part of the function.

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