Fix serial port selection for ATSAM chips

src/lib/DenkoDefines.h

@@ -120,14 +120,10 @@
 // Uses SerialUSB (left port), which is native USB, on Arduino Due & Zero, or Serial otherwise.
 // On many boards, eg. Arduino Leonardo, RP2040, ESP32-S3, Serial is native USB regardless.
 #if defined(__SAM3X8E__) || defined(__SAMD21G18A__)
-  // Prefer native USB, "SerialUSB" (left port on Due and Zero) once available.
-  #if defined(SerialUSB)
-    #define DENKO_SERIAL_IF SerialUSB
-    #define DENKO_USB_CDC
+  #define DENKO_SERIAL_IF SERIAL_PORT_USBVIRTUAL
+  #define DENKO_USB_CDC
   // "Serial" is UART (right port) on Due and Zero, but may be native USB on boards with one port.
-  #else
-    #define DENKO_SERIAL_IF Serial
-  #endif
+  // #define DENKO_SERIAL_IF Serial
 #else
   #define DENKO_SERIAL_IF Serial
 #endif