tinyusb: add function introduced in 0.18

Author: facchinm

Diff for: cores/arduino/usb/USB.cpp

@@ -455,4 +455,8 @@ extern "C"  __attribute((weak))  int32_t tud_msc_scsi_cb (uint8_t lun, uint8_t c
     (void) buffer;
     (void) bufsize;
     return -1;
-}
+}
+
+extern "C" uint32_t tusb_time_millis_api(void) {
+  return millis();
+}