net: hns3: add a check for index in hclge_get_rss_key()

The index is received from vf, if use it directly,
an out-of-bound issue may be caused, so add a check for
this index before using it in hclge_get_rss_key().

Fixes: a638b1d8

 ("net: hns3: fix get VF RSS issue")
Signed-off-by: Yufeng Mo <moyufeng@huawei.com>
Signed-off-by: Huazhong Tan <tanhuazhong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>