va_end for _d function

[controllercustom]

va_end should be used to match va_start. At least every example I have seen of va_list does.

@@ -46,17 +46,18 @@ bool mt_serial_mode = false;
 void _d(const char * fmt, ...) {
   static char vabuf[VA_BUFSIZE];
   va_list ap;
   va_start(ap, fmt);
   vsnprintf(vabuf, sizeof(vabuf), fmt, ap);
+  va_end(ap);
   Serial.println(vabuf);
   Serial.flush();
 }