io_uring: bump poll refs to full 31-bits
The previous commit:
1bc84c40088 ("io_uring: remove poll entry from list when canceling all")
removed a potential overflow condition for the poll references. They
are currently limited to 20-bits, even if we have 31-bits available. The
upper bit is used to mark for cancelation.
Bump the poll ref space to 31-bits, making that kind of situation much
harder to trigger in general. We'll separately add overflow checking
and handling.
Fixes:
aa43477b0402 ("io_uring: poll rework")
Signed-off-by: Jens Axboe <axboe@kernel.dk>