net: hns: Remove redundant mac_get_id()

There is a mac_id in mac control block structure, so the callback
function mac_get_id() is useless. Here we remove this function.

Reported-by: Weiwei Deng <dengweiwei@huawei.com>
Signed-off-by: Kejian Yan <yankejian@huawei.com>
Reviewed-by: Salil Mehta <salil.mehta@huawei.com>
Signed-off-by: Salil Mehta <salil.mehta@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>