ethernet: make more use of device_get_ethdev_address()

Convert a few drivers to device_get_ethdev_address(),
saving a few LoC.

The check if addr is valid in netsec is superfluous,
device_get_ethdev_addr() already checks that (in
fwnode_get_mac_addr()).

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>