ASoC: OMAP McBSP: Remove redundant accessors

We no longer need accessor functions for max_tx/rx_threshold, dma_op_mode
or for the FIFO size.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Tested-by: Grazvydas Ignotas <notasas@gmail.com>
Tested-by: Janusz Krzysztofik <jkrzyszt@tis.icnet.pl>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Jarkko Nikula <jarkko.nikula@bitmer.com>
Signed-off-by: Liam Girdwood <lrg@ti.com>