Move away from gr_surface.

Change-Id: Id23940a2e92bbfd56a2f2e1e021fb89114830dd4
diff --git a/slideshow/slideshow.cpp b/slideshow/slideshow.cpp
index c015d53..318d805 100644
--- a/slideshow/slideshow.cpp
+++ b/slideshow/slideshow.cpp
@@ -54,7 +54,7 @@
 
 static void draw(const char *resname)
 {
-    gr_surface surface;
+    GRSurface* surface;
     int w, h, x, y;
 
     if (res_create_display_surface(resname, &surface) < 0) {