cpumask: use mm_cpumask() wrapper: cris

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>
diff --git a/arch/cris/arch-v32/mm/tlb.c b/arch/cris/arch-v32/mm/tlb.c
index 55ade36..6779bcb 100644
--- a/arch/cris/arch-v32/mm/tlb.c
+++ b/arch/cris/arch-v32/mm/tlb.c
@@ -185,7 +185,7 @@
 		/* Make sure there is a MMU context. */
 		spin_lock(&mmu_context_lock);
 		get_mmu_context(next);
-		cpu_set(cpu, next->cpu_vm_mask);
+		cpumask_set_cpu(cpu, mm_cpumask(next));
 		spin_unlock(&mmu_context_lock);
 
 		/*