If the low level driver has no timeout handler, the
/sys/block/<disk>/queue/io_timeout will not be displayed.
Reviewed-by: NBart Van Assche <bvanassche@acm.org>
Signed-off-by: NWeiping Zhang <zhangweiping@didiglobal.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>