io_uring/tctx: mark io_wq as exiting before error path teardown

io_uring/tctx: mark io_wq as exiting before error path teardown

syzbot reports that it's hitting the below condition for exiting an
io_wq context:

WARN_ON_ONCE(!test_bit(IO_WQ_BIT_EXIT, &wq->state))

in io_wq_put_and_exit(), which can be triggered with memory allocation
fault injection. Ensure that the io_wq is marked as exiting to silence
this warning trigger.

Reported-by: syzbot+79a4cc863a8db58cd92b@syzkaller.appspotmail.com
Fixes: 7880174e1e5e ("io_uring/tctx: clean up __io_uring_add_tctx_node() error handling")
Reviewed-by: Clément Léger <cleger@meta.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>