!6800 block: fix overflow in blk_ioctl_discard()

Merge Pull Request from: @ci-robot 
 
PR sync from: Li Nan <linan122@huawei.com>
https://mailweb.openeuler.org/hyperkitty/list/kernel@openeuler.org/message/QWJOCDRXF23DWNIR4OTXUHH6VJ4E4N7F/ 
 
https://gitee.com/openeuler/kernel/issues/I9K0H3 
 
Link:https://gitee.com/openeuler/kernel/pulls/6800

 

Reviewed-by: Liu YongQiang <liuyongqiang13@huawei.com>
Reviewed-by: Yu Kuai <yukuai3@huawei.com>
Signed-off-by: Zhang Changzhong <zhangchangzhong@huawei.com>