dmaengine: at_hdmac: Rename "dma_common" to "dma_device"

"dma_common" name was misleading and did not suggest that's actually
a struct dma_device underneath. Rename it so that readers can follow the
code easier. One may see some checks and a warning when running
checkpatch. Those have nothing to do with the rename and will be addressed
in a further patch.

Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Link: https://lore.kernel.org/r/20221025090306.297886-1-tudor.ambarus@microchip.com
Link: https://lore.kernel.org/r/20221025090306.297886-30-tudor.ambarus@microchip.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>