net: stmmac: Adjust dump offset of DMA registers for ethtool

The commit fbf68229 ("net: stmmac: unify registers dumps methods")

in the Linux kernel modified the register dump to store the DMA registers
at the DMA register offset (0x1000) but ethtool (stmmac.c) looks for the
DMA registers after the MAC registers which is offset 55.
This patch copies the DMA registers from the higher offset to the offset
where ethtool expects them.

Signed-off-by: Thor Thayer <thor.thayer@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>