usb_ep_disable — endpoint is no longer usable
| int usb_ep_disable ( | struct usb_ep * ep ); | 
   no other task may be using this endpoint when this is called.
   any pending and uncompleted requests will complete with status
   indicating disconnect (-ESHUTDOWN) before this call returns.
   gadget drivers must call usb_ep_enable again before queueing
   requests to the endpoint.
   
returns zero, or a negative error code.