fix(vd960DBN): MQTTPacket_connectData_initializer 不能用于赋值，用临时变量中转

vd960DBN/BLE/OnlyUpdateApp_Peripheral/APP/iot_mqtt_srv.c

@@ -81,7 +81,8 @@ static int iot_mqtt_send_connect(void) {
     static uint8_t buf[256];             // static: 避免 256字节栈开销
     int len;
 
-    opts = MQTTPacket_connectData_initializer;
+    // struct assignment 不支持 brace initializer，用临时变量中转
+    { MQTTPacket_connectData _init = MQTTPacket_connectData_initializer; opts = _init; }
 
     opts.MQTTVersion = 4;   // MQTT 3.1.1
     opts.keepAliveInterval = IOT_MQTT_KEEPALIVE_SEC;