dmaengine: i.MX: Fix merge of cookie branch.

When merging DMA cookie changes a small chunk
of code was dropped. This broke imx-dma driver.

This patch adds this chunk again and fixes the problem.

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