Merge pull request #504 from mjs513/master

Update usb.c so MTP_repsonder can work at 600Mhz

teensy4/usb.c

@@ -999,7 +999,7 @@ void usb_receive(int endpoint_number, transfer_t *transfer)
 
 uint32_t usb_transfer_status(const transfer_t *transfer)
 {
-#if 0
+#if #ifdef USB_MTPDISK
 	uint32_t status, cmd;
 	//int count=0;
 	cmd = USB1_USBCMD;