When add flow director fule for vf, the vf id is used as array
subscript before valid checking, which may cause memory overflow.

Fixes: dd74f815 ("net: hns3: Add support for rule add/delete for flow director")
Signed-off-by: Jian Shen <shenjian15@huawei.com>
Signed-off-by: Peng Li <lipeng321@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>