net: hns3: replace num_req_vfs with num_alloc_vport in hclge_reset_umv_space()

Like the calculation elsewhere, replaces num_req_vfs with
num_alloc_vport in hclge_reset_umv_space().

Signed-off-by: Jian Shen <shenjian15@huawei.com>
Signed-off-by: Huazhong Tan <tanhuazhong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>