net: hns3: fix incorrect resp_msg issue

In hclge_mbx_handler(), if there are two consecutive mailbox
messages that requires resp_msg, the resp_msg is not cleared
after processing the first message, which will cause the resp_msg
data of second message incorrect.

Fix it by clearing the resp_msg before processing every mailbox
message.

Fixes: bb5790b7

 ("net: hns3: refactor mailbox response scheme between PF and VF")
Signed-off-by: Jiaran Zhang <zhangjiaran@huawei.com>
Signed-off-by: Huazhong Tan <tanhuazhong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>