Fix arduino sketch

Author: marqdevx

content/hardware/04.pro/shields/portenta-vision-shield/tutorials/vs-ard-gs/content.md

@@ -54,6 +54,8 @@ HM01B0 himax;
 Camera cam(himax);
 #define IMAGE_MODE CAMERA_GRAYSCALE
 FrameBuffer fb(320,240,2);
+
+unsigned long lastUpdate = 0;
 ```
 
 In the `setup()` function, let's start the Serial communication at `921600` baud rate and initialize the camera using `cam.begin()`. 
@@ -270,6 +272,8 @@ Camera cam(himax);
 #define IMAGE_MODE CAMERA_GRAYSCALE
 FrameBuffer fb(320,240,2);
 
+unsigned long lastUpdate = 0;
+
 void setup() {
   Serial.begin(921600);
   //Init the cam QVGA, 30FPS