dmaengine: ioatdma: fixup ioatdma_device namings

Changing the variable names for ioatdma_device to be consistently named
ioat_dma instead of device/dma in order to avoid confusion and distinct
from struct device. This will clearly indicate that it is an
ioatdma_device. This also make all the naming consistent that the dma
device is ioat_dma and all the channels are ioat_chan.

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>