ASoC: ti: davinci-mcasp: Set unused serializers as INACTIVE

Unused serializers needs to be configured as INACTIVE, otherwise they will
underflow/overflow when multiple serializers are connected, but some are
not needed for the given stream.

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