__uvc_ctrl_get
ret = __uvc_ctrl_get(chain, master_ctrl, master_map, &val);
ret = __uvc_ctrl_get(chain, master_ctrl, master_map,
__uvc_ctrl_get(chain, ctrl, mapping, &val) == 0)
__uvc_ctrl_get(handle->chain, ctrl, mapping, &val) == 0)
return __uvc_ctrl_get(chain, ctrl, mapping, &xctrl->value);