ASoC: davinci-mcasp: Validate tdm_slots parameter at probe time

Instead of validating the tdm_slots parameter every time at hw_params we
can do it once during probe. If the parameter is not valid (<2 or >32)
print an error and fix it up.

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