const: mark struct vm_struct_operations

* mark struct vm_area_struct::vm_ops as const
* mark vm_ops in AGP code

But leave TTM code alone, something is fishy there with global vm_ops
being used.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/misc/sgi-gru/grufile.c

@@ -438,7 +438,7 @@ static struct miscdevice gru_miscdev = {
 	.fops		= &gru_fops,
 };
 
-struct vm_operations_struct gru_vm_ops = {
+const struct vm_operations_struct gru_vm_ops = {
 	.close		= gru_vma_close,
 	.fault		= gru_fault,
 };