net: hns3: fix the logic for clearing resp_msg

driver inclusion
category: bugfix
bugzilla: NA
CVE: NA

----------------------------

In the hclge_mbx_handler function, if there are two consecutive mailbox
messages that require resp_msg, the first message's resp_msg is not
cleared after being processed, causing the second resp_msg data is
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: Yonglong Liu <liuyonglong@huawei.com>
Reviewed-by: li yongxin <liyongxin1@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>