Fix variable size.

src/main.c

@@ -333,7 +333,7 @@ static void btnProcess(void) {
 }
 
 static void tubeRefresh(void) {
-  static int cnt = 0;
+  static uint8_t cnt = 0;
 
   /* We start ourselves every 125 ms to update 8 digits in a second. */
   if (cnt == 0) {