net: hns3: check msg_data before memcpy in hclgevf_send_mbx_msg

The value of msg_data may be NULL in some cases, which will cause
errors reported by some compiler.

So this patch adds a check to fix it.
Signed-off-by: Weihang Li <liweihang@hisilicon.com>
Signed-off-by: Peng Li <lipeng321@huawei.com>
Signed-off-by: Huazhong Tan <tanhuazhong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

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

@@ -102,6 +102,7 @@ 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;
+	if (msg_data)
 		memcpy(&req->msg[2], msg_data, msg_len);
 
 	/* synchronous send */