ASoC: DaVinci: i2s, reduce underruns by combining into 1 element

Allow the left and right 16 bit samples to be shifted out as 1
32 bit sample.

Signed-off-by: Troy Kisky <troy.kisky@boundarydevices.com>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>