net/mlx5e: Switch to kmemdup() when allocate dev_addr

Use kmemdup() helper instead of open-coding to
simplify the code when allocate dev_addr.

Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Acked-by: Saeed Mahameed <saeedm@nvidia.com>
Link: https://lore.kernel.org/r/20220914140100.3795545-2-yangyingliang@huawei.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>