dmaengine: pl330: Handle xferred count if DMAMOV hasn't finished

After executing DMAGO it's possible that a request can come in for the
current xferred count, but if that happens too soon then DMAMOV SAR/DAR
may not have yet completed. If that happens, we should explicitly return 0
since nothing has been transferred yet.

Signed-off-by: Stephen Barber <smbarber@chromium.org>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>