io_uring: don't use int for ABI

io_uring: don't use int for ABI

__kernel_rwf_t is defined as int, the actual size of which is
implementation defined. It won't go well if some compiler / archs
ever defines it as i64, so replace it with __u32, hoping that
there is no one using i16 for it.

Cc: stable@vger.kernel.org
Fixes: 2b188cc1bb857 ("Add io_uring IO interface")
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/47c666c4ee1df2018863af3a2028af18feef11ed.1751412511.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>