[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/ops_address.c b/fs/gfs2/ops_address.c
index 207363a..26db333 100644
--- a/fs/gfs2/ops_address.c
+++ b/fs/gfs2/ops_address.c
@@ -655,7 +655,7 @@
 				    DIO_OWN_LOCKING);
 }
 
-struct address_space_operations gfs2_file_aops = {
+const struct address_space_operations gfs2_file_aops = {
 	.writepage = gfs2_writepage,
 	.readpage = gfs2_readpage,
 	.readpages = gfs2_readpages,