dmaengine: pxa_dma: fix debug message

In a very tight timeframe, the debug message in the transfer completion
handler can be misleading, as the completion test report can change just
after the message, and the code flow cannot be deduced from the debug
message.

This is just a cleanup to make debugging easier.

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>