io_uring: use separate list entry for iopoll requests

A previous commit ended up enabling file tracking for iopoll requests,
which conflicts with both of them using the same list entry for tracking.
Add a separate list entry just for iopoll requests, avoid this issue.

No upstream commit exists for this issue.

Reported-by: Greg Thelen <gthelen@google.com>
Fixes: df3f3bb5 ("io_uring: add missing item types for various requests")
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>