net: hns3: check msg_data before memcpy

driver inclusion
category: bugfix
bugzilla: NA
CVE: NA

Value of msg_data is NULL in some situation, which may cause errors reported
from some complier.

Feature or Bugfix: Bugfix
Signed-off-by: Nliweihang <liweihang@huawei.com>
Reviewed-by: Nlipeng <lipeng321@huawei.com>
Reviewed-by: NYang Yingliang <yangyingliang@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

drivers/net/ethernet/hisilicon/hns3/hns3vf/hclgevf_mbx.c

@@ -129,7 +129,8 @@ int hclgevf_send_mbx_msg(struct hclgevf_dev *hdev, u16 code, u16 subcode,
 					  ~HCLGE_MBX_NEED_RESP_BIT;
 	req->msg[0] = code;
 	req->msg[1] = subcode;
-	memcpy(&req->msg[2], msg_data, msg_len);
+	if (msg_data)
+		memcpy(&req->msg[2], msg_data, msg_len);
 
 	/* synchronous send */
 	if (need_resp) {