io_uring: only call io_should_terminate_tw() once for ctx

io_uring: only call io_should_terminate_tw() once for ctx

io_fallback_req_func() calls io_should_terminate_tw() on each req's ctx.
But since the reqs all come from the ctx's fallback_llist, req->ctx will
be ctx for all of the reqs. Therefore, compute ts.cancel as
io_should_terminate_tw(ctx) just once, outside the loop.

Signed-off-by: Caleb Sander Mateos <csander@purestorage.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>