dmaengine: at_hdmac: Rename "chan_common" to "dma_chan"

"chan_common" was misleading and did not suggest that's actually
a struct dma_chan underneath. Rename it so that readers can follow the
code easier. One may see some checks 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/20221025090306.297886-31-tudor.ambarus@microchip.com


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