virtio/virtio-balloon: Prefer Object* over void* parameter

*opaque is an alias to *obj. Using the ladder makes the code consistent with
with other devices, e.g. accel/kvm/kvm-all and accel/tcg/tcg-all. It also
makes the cast more typesafe.

Signed-off-by: Bernhard Beschow <shentey@gmail.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Message-Id: <20220301222301.103821-2-shentey@gmail.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

hw/virtio/virtio-balloon.c

@@ -242,7 +242,7 @@ static void balloon_stats_get_all(Object *obj, Visitor *v, const char *name,
                                   void *opaque, Error **errp)
 {
     Error *err = NULL;
-    VirtIOBalloon *s = opaque;
+    VirtIOBalloon *s = VIRTIO_BALLOON(obj);
     int i;
 
     if (!visit_start_struct(v, name, NULL, 0, &err)) {
@@ -277,7 +277,7 @@ static void balloon_stats_get_poll_interval(Object *obj, Visitor *v,
                                             const char *name, void *opaque,
                                             Error **errp)
 {
-    VirtIOBalloon *s = opaque;
+    VirtIOBalloon *s = VIRTIO_BALLOON(obj);
     visit_type_int(v, name, &s->stats_poll_interval, errp);
 }
 
@@ -285,7 +285,7 @@ static void balloon_stats_set_poll_interval(Object *obj, Visitor *v,
                                             const char *name, void *opaque,
                                             Error **errp)
 {
-    VirtIOBalloon *s = opaque;
+    VirtIOBalloon *s = VIRTIO_BALLOON(obj);
     int64_t value;
 
     if (!visit_type_int(v, name, &value, errp)) {
@@ -1015,12 +1015,12 @@ static void virtio_balloon_instance_init(Object *obj)
     s->free_page_hint_notify.notify = virtio_balloon_free_page_hint_notify;
 
     object_property_add(obj, "guest-stats", "guest statistics",
-                        balloon_stats_get_all, NULL, NULL, s);
+                        balloon_stats_get_all, NULL, NULL, NULL);
 
     object_property_add(obj, "guest-stats-polling-interval", "int",
                         balloon_stats_get_poll_interval,
                         balloon_stats_set_poll_interval,
-                        NULL, s);
+                        NULL, NULL);
 }
 
 static const VMStateDescription vmstate_virtio_balloon = {