refractor usbd-dcd callback, add bus event isr

demos/device/device_os_none/cdcd_app.c

@@ -117,10 +117,10 @@ void tusbd_cdc_xfer_isr(uint8_t coreid, tusb_event_t event, cdc_pipeid_t pipe_id
 
 OSAL_TASK_FUNCTION( cdcd_serial_app_task ) (void* p_task_para)
 {
-  tusb_error_t error;
-
   OSAL_TASK_LOOP_BEGIN
 
+  tusb_error_t error;
+
   osal_semaphore_wait(sem_hdl, OSAL_TIMEOUT_WAIT_FOREVER, &error);
 
   if ( tusbd_cdc_is_configured(0) )