iiod: Cancel buffer before freeing it

This should stop any pending block enqueue/dequeue operations, making it
possible to destroy the buffer without waiting for I/O to finish.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>

iiod/responder.c

@@ -47,6 +47,8 @@ static void free_buffer_entry(struct buffer_entry *entry)
 {
 	struct block_entry *block_entry, *block_next;
 
+	iio_buffer_cancel(entry->buf);
+
 	if (!NO_THREADS) {
 		iio_task_stop(entry->dequeue_task);
 		iio_task_stop(entry->enqueue_task);