x86: change _node_to_cpumask_ptr to return const ptr

* Strengthen the return type for the _node_to_cpumask_ptr to be
    a const pointer.  This adds compiler checking to insure that
    node_to_cpumask_map[] is not changed inadvertently.

Signed-off-by: Mike Travis <travis@sgi.com>
Cc: "akpm@linux-foundation.org" <akpm@linux-foundation.org>
Cc: Yinghai Lu <yhlu.kernel@gmail.com>
Acked-by: Vegard Nossum <vegard.nossum@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

include/asm-generic/topology.h

@@ -60,7 +60,8 @@
 #ifndef node_to_cpumask_ptr
 
 #define	node_to_cpumask_ptr(v, node) 					\
-		cpumask_t _##v = node_to_cpumask(node), *v = &_##v
+		cpumask_t _##v = node_to_cpumask(node);			\
+		const cpumask_t *v = &_##v
 
 #define node_to_cpumask_ptr_next(v, node)				\
 			  _##v = node_to_cpumask(node)