net: hns3: remove unused hclge_ring_to_dma_dir

hclge_ring_to_dma_dir is unused anywhere.
This patch removes it.

Signed-off-by: Huazhong Tan <tanhuazhong@huawei.com>
Signed-off-by: Peng Li <lipeng321@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>