xen/grant-table: constify gnttab_ops structure

The gnttab_ops structure is never modified, so declare it as const.

Done with the help of Coccinelle.
Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>

drivers/xen/grant-table.c

@@ -128,7 +128,7 @@ struct unmap_refs_callback_data {
 	int result;
 };
 
-static struct gnttab_ops *gnttab_interface;
+static const struct gnttab_ops *gnttab_interface;
 
 static int grant_table_version;
 static int grefs_per_grant_frame;
@@ -1013,7 +1013,7 @@ static int gnttab_map(unsigned int start_idx, unsigned int end_idx)
 	return rc;
 }
 
-static struct gnttab_ops gnttab_v1_ops = {
+static const struct gnttab_ops gnttab_v1_ops = {
 	.map_frames			= gnttab_map_frames_v1,
 	.unmap_frames			= gnttab_unmap_frames_v1,
 	.update_entry			= gnttab_update_entry_v1,