io_uring: run local task_work from ring exit IOPOLL reaping

In preparation for needing to shift NVMe passthrough to always use
task_work for polled IO completions, ensure that those are suitably
run at exit time. See commit:

9ce6c987 ("nvme: always punt polled uring_cmd end_io work to task_work")

for details on why that is necessary.

Signed-off-by: Jens Axboe <axboe@kernel.dk>