media: imx: imx7-media-csi: Rename phys variables to dma_addr

All the phys variables and structure fields store a DMA address, not a
physical address. Even if the two are effectively identical on all
platforms where this driver is used due to the lack of IOMMU, rename the
variables to dma_addr to make their usage clearer.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Paul Elder <paul.elder@ideasonboard.com>
Acked-by: Rui Miguel Silva <rmfrfs@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>