qlnxe: Avoid memcpy with same source and destination
In case the device is VF, qlnx_get_mac_addr() returns ha->primary_mac
hence it ends up memcpy with same source and destination. Refactor
slightly to avoid that.
Reviewed by: kbowling
MFC after: 5 days
Differential Revision: https://reviews.freebsd.org/D54884