dmaengine: ioatdma: fixup kernel doc errors from dma.h

./scripts/kerne-doc is reporting errors on dma.h. Clean up all reported
errors.

Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Acked-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>