dmaengine: edma: Correct the handling of src/dst_maxburst == 0

When clients asks for maxburst = 0 it is basically the same case as if they
were asking for maxburst = 1 since in both case ASYNC need to be used and
the eDMA is expected to write/read one word per DMA request.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Acked-by: Joel Fernandes <joelf@ti.com>
Reviewed-and-Tested-by: Joel Fernandes <joelf@ti.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>