etherdevice: use __dev_addr_set()

Andrew points out that eth_hw_addr_set() replaces memcpy()
calls so we can't use ether_addr_copy() which assumes
both arguments are 2-bytes aligned.

Reported-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>