ASoC: ab8500-codec: Set rx dai slots from rx_mask

Replace hard coded rx slot numbers from ab8500_codec_set_dai_tdm_slot
using the ones requested by the machine driver in rx_mask instead.

Signed-off-by: Fabio Baltieri <fabio.baltieri@linaro.org>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>