io_uring: fix double io_uring free

Once we created a file for current context during setup, we should not
call io_ring_ctx_wait_and_kill() directly as it'll be done by fput(file)

Cc: stable@vger.kernel.org # 5.10
Reported-by:  <syzbot+c9937dfb2303a5f18640@syzkaller.appspotmail.com>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
[axboe: fix unused 'ret' for !CONFIG_UNIX]
Signed-off-by: Jens Axboe <axboe@kernel.dk>