commit e977d6d34f0c08e3c3b132c9e73b98d0db50abc1 upstream.

We're going to need this helper in a future patch, so move it out
of io_async_cancel() and into its own separate function.

No functional changes in this patch.
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Reviewed-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>