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.