checkpatch: ignore request to use ether_addr_copy()

The Linux kernel, from which checkpatch originates, contains function
ether_addr_copy() to copy Ethernet MAC addresses, and checkpatch warns
that it should be used in preference to memcpy() where appropriate.
U-Boot doesn't contain ether_addr_copy(), so tell checkpatch not to issue
this warning.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Reviewed-by: Marek Vasut <marex@denx.de>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
Tested-by: Anand Moon <linux.amoon@gmail.com>
Reviewed-by: Anand Moon <linux.amoon@gmail.com>