[GFS2] Make our address_space_operations const

As per Christoph's patch:
http://www.kernel.org/git/?p=linux/kernel/git/steve/gfs2-2.6.git;a=commitdiff;h=f5e54d6e53a20cef45af7499e86164f0e0d16bb2

We mark struct address_space_operations const in GFS2.

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
diff --git a/fs/gfs2/meta_io.c b/fs/gfs2/meta_io.c
index 2523d42..ddcd4dc 100644
--- a/fs/gfs2/meta_io.c
+++ b/fs/gfs2/meta_io.c
@@ -159,7 +159,7 @@
 	return try_to_free_buffers(page);
 }
 
-static struct address_space_operations aspace_aops = {
+static const struct address_space_operations aspace_aops = {
 	.writepage = gfs2_aspace_writepage,
 	.releasepage = gfs2_aspace_releasepage,
 };