To avoid race with vchan_complete, use the race free way to terminate
running transfer.

Implement the device_synchronize callback to make sure that the terminated
descriptor is freed.
Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>