qom: Make type checker functions accept const pointers

The existing type check macros all unconditionally drop const
qualifiers from their arguments.  Keep this behavior in the
macros generated by DECLARE_*CHECKER* by now.

Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Message-Id: <20200831210740.126168-6-ehabkost@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>

include/qom/object.h

@@ -567,7 +567,7 @@ struct Object
  */
 #define DECLARE_INSTANCE_CHECKER(InstanceType, OBJ_NAME, TYPENAME) \
     static inline G_GNUC_UNUSED InstanceType * \
-    OBJ_NAME(void *obj) \
+    OBJ_NAME(const void *obj) \
     { return OBJECT_CHECK(InstanceType, obj, TYPENAME); }
 
 /**
@@ -584,11 +584,11 @@ struct Object
  */
 #define DECLARE_CLASS_CHECKERS(ClassType, OBJ_NAME, TYPENAME) \
     static inline G_GNUC_UNUSED ClassType * \
-    OBJ_NAME##_GET_CLASS(void *obj) \
+    OBJ_NAME##_GET_CLASS(const void *obj) \
     { return OBJECT_GET_CLASS(ClassType, obj, TYPENAME); } \
     \
     static inline G_GNUC_UNUSED ClassType * \
-    OBJ_NAME##_CLASS(void *klass) \
+    OBJ_NAME##_CLASS(const void *klass) \
     { return OBJECT_CLASS_CHECK(ClassType, klass, TYPENAME); }
 
 /**