net: sh_eth: Pass sh_eth_dev around

Pass sh_eth_dev structure around instead of eth_device, since the
later is specific to the legacy networking support. This change is
done in preparation for the DM addition.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>
Cc: Joe Hershberger <joe.hershberger@ni.com>