net: hns3: add a conversion for mailbox's response code

Currently, when mailbox handling fails, the PF driver
just responds 1 to the VF driver. It is not sufficient
for the VF driver to find out why its mailbox fails.

So the error should be responded to VF, but the error
is type int and the response field in struct
hclge_mbx_pf_to_vf_cmd is type u16, a conversion is
needed.

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>