omapfb: Blizzard: fix pointer to be const

Fixes a compiler warning:
warning: assignment discards qualifiers from pointer target type

Cc: Tomi Valkeinen <tomi.valkeinen@nokia.com>
Cc: Imre Deak <imre.deak@nokia.com>
Signed-off-by: Tommi Rantala <tt.rantala@gmail.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>

drivers/video/omap/blizzard.c

@@ -191,7 +191,7 @@ struct blizzard_struct {
 
 	struct omapfb_device	*fbdev;
 	struct lcd_ctrl_extif	*extif;
-	struct lcd_ctrl		*int_ctrl;
+	const struct lcd_ctrl	*int_ctrl;
 
 	void			(*power_up)(struct device *dev);
 	void			(*power_down)(struct device *dev);