Add debug trace for io_u_queue_complete()

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/io_u.c b/io_u.c
index 42ad37b..bd7df0c 100644
--- a/io_u.c
+++ b/io_u.c
@@ -883,6 +883,8 @@
 	int ret;
 	struct timespec ts = { .tv_sec = 0, .tv_nsec = 0, };
 
+	dprint(FD_IO, "io_u_queued_completed: min=%d\n", min_events);
+
 	if (!min_events)
 		tvp = &ts;