savevm: Add DeviceState param

When available, we'd like to be able to access the DeviceState
when registering a savevm.  For buses with a get_dev_path()
function, this will allow us to create more unique savevm
id strings.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
diff --git a/audio/audio.c b/audio/audio.c
index dbf0b96..ad51077 100644
--- a/audio/audio.c
+++ b/audio/audio.c
@@ -1901,7 +1901,7 @@
     }
 
     QLIST_INIT (&s->card_head);
-    vmstate_register (0, &vmstate_audio, s);
+    vmstate_register (NULL, 0, &vmstate_audio, s);
 }
 
 void AUD_register_card (const char *name, QEMUSoundCard *card)