const: mark remaining address_space_operations const

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 8b81927..6c41731 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -772,7 +772,7 @@
 	}
 }
 
-static struct address_space_operations btree_aops = {
+static const struct address_space_operations btree_aops = {
 	.readpage	= btree_readpage,
 	.writepage	= btree_writepage,
 	.writepages	= btree_writepages,