When desc filling fails in hns3_nic_net_xmit, it will call
hns3_clear_desc to unmap the dma mapping. But currently the
ring->next_to_use points to the desc where the desc filling
or dma mapping return error, which means the desc that
ring->next_to_use points to has not done the dma mapping,
the desc that need unmapping is before the ring->next_to_use.

This patch fixes it by calling ring_ptr_move_bw(next_to_use)
before doing unmapping operation, and set desc_cb->dma to
zero to avoid freeing it again when unloading.

Also, when filling skb head or frag fails, both need to unmap
all the way back to next_to_use_head, so remove one desc filling
error handling.

Fixes: 76ad4f0e ("net: hns3: Add support of HNS3 Ethernet Driver for hip08 SoC")
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>