[sysprof] visualizer: use cast macro with type check

[Christian Hergert <chergert src gnome org>]

commit 6a3d7282ec737d5fd0d97427fb6bcf1c7de6585a
Author: Christian Hergert <chergert redhat com>
Date:   Fri Feb 17 00:20:13 2017 -0800

    visualizer: use cast macro with type check

 lib/sp-visualizer-ticks.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/lib/sp-visualizer-ticks.c b/lib/sp-visualizer-ticks.c
index fb3b638..cfa5f88 100644
--- a/lib/sp-visualizer-ticks.c
+++ b/lib/sp-visualizer-ticks.c
@@ -233,7 +233,7 @@ static gboolean
 sp_visualizer_ticks_draw (GtkWidget *widget,
                           cairo_t   *cr)
 {
-  SpVisualizerTicks *self = (SpVisualizerTicks *)widget;
+  SpVisualizerTicks *self = SP_VISUALIZER_TICKS (widget);
   GtkStyleContext *style;
   GtkAllocation alloc;
   GtkStateFlags state;