io_uring: flush delayed fallback task_work in cancelation

Just like we run the inline task_work, ensure we also factor in and
run the fallback task_work.
Signed-off-by: Jens Axboe <axboe@kernel.dk>

io_uring/io_uring.c

@@ -3218,6 +3218,8 @@ static __cold bool io_uring_try_cancel_requests(struct io_ring_ctx *ctx,
 	ret |= io_kill_timeouts(ctx, task, cancel_all);
 	if (task)
 		ret |= io_run_task_work() > 0;
+	else
+		ret |= flush_delayed_work(&ctx->fallback_work);
 	return ret;
 }