dmaengine: omap-dma: Correct type2 descriptor's member types

The type of CDEI, CSEI, CDFI and CSFI is signed.
This did not caused issue so far as we only use unsigned values.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>