dmaengine: imx-dma: dont complete descriptor for cyclic dma

the cookie updates completed the cyclic dma descriptor wrongly. This caused the
BUG_ON to be hit as submit is called for completed descriptor

Fix this by not marking the cyclic descriptor as complete

Tested-by: Javier Martin <javier.martin@vista-silicon.com>
Signed-off-by: Vinod Koul <vinod.koul@linux.intel.com>