io_uring: fix iowq_limits data race in tctx node addition

io_uring: fix iowq_limits data race in tctx node addition

__io_uring_add_tctx_node() reads ctx->int_flags and
ctx->iowq_limits[0..1] without holding ctx->uring_lock, while
io_register_iowq_max_workers() writes these same fields under the lock.

Mostly an application problem if you try and make these race, but let's
silence KCSAN by just grabbing the ->uring_lock around the operation.
This is a slow path operation anyway, and ->uring_lock will be grabbed
by submission right after anyway.

Fixes: 2e480058ddc2 ("io-wq: provide a way to limit max number of workers")
Signed-off-by: Jens Axboe <axboe@kernel.dk>