Properly escape QDECREF macro arguments

QDECREF does not properly escape the macro arguments which can lead to
unexpected syntax errors.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
diff --git a/qobject.h b/qobject.h
index 4cc9287..76f669f 100644
--- a/qobject.h
+++ b/qobject.h
@@ -60,7 +60,7 @@
     QObject base
 
 /* Get the 'base' part of an object */
-#define QOBJECT(obj) (&obj->base)
+#define QOBJECT(obj) (&(obj)->base)
 
 /* High-level interface for qobject_incref() */
 #define QINCREF(obj)      \