Method writeback_val

dnn/src/common/roi_align_helper.h:94–94

        }
    }
    MEGDNN_HOST MEGDNN_DEVICE void writeback_val(T& val) { val = cnt > 0 ? maxval : 0; }
    MEGDNN_HOST MEGDNN_DEVICE void writeback_idx(int& idx) { idx = maxidx; }
};