ASoC: omap-pcm: Select sDMA synchronization based on packet_size

Since we only have element or packet synchronization we can use the
dma_data->packet_size to select the desired mode:
if packet_size is 0 we use ELEMENT mode
if packet_size is not 0 we use PACKET mode for sDMA synchronization.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Tested-by: Janusz Krzysztofik <jkrzyszt@tis.icnet.pl>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>