ocfs2: constify ocfs2_extent_tree_operations structures

The ocfs2_extent_tree_operations structures are never modified, so
declare them as const.

Done with the help of Coccinelle.

Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Cc: Mark Fasheh <mfasheh@suse.de>
Cc: Joel Becker <jlbec@evilplan.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/ocfs2/alloc.h b/fs/ocfs2/alloc.h
index fb09b97..f3dc1b0 100644
--- a/fs/ocfs2/alloc.h
+++ b/fs/ocfs2/alloc.h
@@ -54,7 +54,7 @@
  */
 struct ocfs2_extent_tree_operations;
 struct ocfs2_extent_tree {
-	struct ocfs2_extent_tree_operations	*et_ops;
+	const struct ocfs2_extent_tree_operations *et_ops;
 	struct buffer_head			*et_root_bh;
 	struct ocfs2_extent_list		*et_root_el;
 	struct ocfs2_caching_info		*et_ci;