net: hns3: some cleanup for struct hns3_enet_ring

This patch removes some unused field in struct hns3_enet_ring,
use ring->dev for ring_to_dev macro, and use dev consistently
in hns3_fill_desc.

Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
Signed-off-by: Huazhong Tan <tanhuazhong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>