util: json: Make first argument of virJSONValueObjectForeachKeyValue const

The iterator function (second argument) already requires that the object
is handled as 'const' thus we won't modify the object itself.

src/util/virjson.c

@@ -1220,7 +1220,7 @@ virJSONValueObjectIsNull(virJSONValuePtr object,
  * during iteration and -1 on generic errors.
  */
 int
-virJSONValueObjectForeachKeyValue(virJSONValuePtr object,
+virJSONValueObjectForeachKeyValue(const virJSONValue *object,
                                   virJSONValueObjectIteratorFunc cb,
                                   void *opaque)
 {

src/util/virjson.h

@@ -167,7 +167,7 @@ typedef int (*virJSONValueObjectIteratorFunc)(const char *key,
                                               const virJSONValue *value,
                                               void *opaque);
 
-int virJSONValueObjectForeachKeyValue(virJSONValuePtr object,
+int virJSONValueObjectForeachKeyValue(const virJSONValue *object,
                                       virJSONValueObjectIteratorFunc cb,
                                       void *opaque);