net: hns3: fix the descriptor index when get rss type

Driver gets rss information from the last descriptor of the packet.
When driver handle the rss type, ring->next_to_clean indicates the
first descriptor of next packet.

This patch fix the descriptor index with "ring->next_to_clean - 1".

Fixes: 232fc64b ("net: hns3: Add HW RSS hash information to RX skb")
Signed-off-by: Peng Li <lipeng321@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>