ASoC: OMAP: Remove sync_mode from omap_pcm_dma_data struct

The omap-pcm platform driver no longer needs this parameter to select
between ELEMENT and PACKET mode. The selection is based on the configured
packet_size.

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>