OMAPDSS: DISPC: Constify omap_overlay_info in dispc_ovl_setup()

The struct omap_overlay_info passed to dispc_ovl_setup() is used to configure
DISPC registers. It shouldn't modify the overlay_info structure. The pos_y field
was being changed in dispc_ovl_setup in the case of interlaced displays. Fix
this and const qualifier to the omap_overlay_info argument.

Signed-off-by: Archit Taneja <archit@ti.com>
diff --git a/drivers/video/omap2/dss/dss.h b/drivers/video/omap2/dss/dss.h
index a14528b..e71a6f1 100644
--- a/drivers/video/omap2/dss/dss.h
+++ b/drivers/video/omap2/dss/dss.h
@@ -444,7 +444,7 @@
 void dispc_ovl_compute_fifo_thresholds(enum omap_plane plane,
 		u32 *fifo_low, u32 *fifo_high, bool use_fifomerge,
 		bool manual_update);
-int dispc_ovl_setup(enum omap_plane plane, struct omap_overlay_info *oi,
+int dispc_ovl_setup(enum omap_plane plane, const struct omap_overlay_info *oi,
 		bool replication, const struct omap_video_timings *mgr_timings);
 int dispc_ovl_enable(enum omap_plane plane, bool enable);
 void dispc_ovl_set_channel_out(enum omap_plane plane,