To signal an successful attach attempt we set the ref counter
of the parent, i.e., the dummy pci bus and check that in our
'probe_cfdata' function.

--- a/dev/pci/azalia.c
+++ b/dev/pci/azalia.c
@@ -591,6 +591,7 @@
 
 	audio_attach_mi(&azalia_hw_if, sc, NULL, &sc->dev);
 
+	parent->dv_ref = 1;
 	return;
 
 err_exit: