net: hns3: clear param in ring when free ring

Param pending_buf and skb may be not NULL when free ring.
This patch clears them when free ring.

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