cpumask: Use mm_cpumask() wrapper instead of cpu_vm_mask

Makes code futureproof against the impending change to mm->cpu_vm_mask.

It's also a chance to use the new cpumask_ ops which take a pointer
(the older ones are deprecated, but there's no hurry for arch code).

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
diff --git a/arch/powerpc/include/asm/mmu_context.h b/arch/powerpc/include/asm/mmu_context.h
index ab4f192..b706366 100644
--- a/arch/powerpc/include/asm/mmu_context.h
+++ b/arch/powerpc/include/asm/mmu_context.h
@@ -31,7 +31,7 @@
 			     struct task_struct *tsk)
 {
 	/* Mark this context has been used on the new CPU */
-	cpu_set(smp_processor_id(), next->cpu_vm_mask);
+	cpumask_set_cpu(smp_processor_id(), mm_cpumask(next));
 
 	/* 32-bit keeps track of the current PGDIR in the thread struct */
 #ifdef CONFIG_PPC32