io_uring: move apoll->events cache

io_uring: move apoll->events cache

In preparation for fixing a regression with pulling in an extra cacheline
for IO that doesn't usually touch the last cacheline of the io_kiocb,
move the cached location of apoll->events to space shared with some other
completion data. Like cflags, this isn't used until after the request
has been completed, so we can piggy back on top of comp_list.

Fixes: 81459350d581 ("io_uring: cache req->apoll->events in req->cflags")
Signed-off-by: Jens Axboe <axboe@kernel.dk>