[gegl] fix use of const qualifier

[Nils Philippsen <nphilipp src gnome org>]

commit 4d6f918f1803d1227452834c604afc85e1fef1cc
Author: Nils Philippsen <nils redhat com>
Date:   Fri Feb 19 15:12:33 2010 +0100

    fix use of const qualifier

 operations/workshop/mirrors.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/operations/workshop/mirrors.c b/operations/workshop/mirrors.c
index 08f8ba1..f783b2a 100644
--- a/operations/workshop/mirrors.c
+++ b/operations/workshop/mirrors.c
@@ -126,7 +126,7 @@ apply_mirror (double mirror_angle,
               GeglRectangle *in_boundary,
               GeglBuffer *dst,
               GeglRectangle *boundary,
-              GeglRectangle *roi)
+              const GeglRectangle *roi)
 {
   const GeglRectangle *src_extent;
   const GeglRectangle *dst_extent;