[S390] cpumask: use mm_cpumask() wrapper

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: Martin Schwidefsky <schwidefsky@de.ibm.com>
diff --git a/arch/s390/mm/pgtable.c b/arch/s390/mm/pgtable.c
index 9bf8612..be6c1cf 100644
--- a/arch/s390/mm/pgtable.c
+++ b/arch/s390/mm/pgtable.c
@@ -296,7 +296,7 @@
 	tsk->mm = tsk->active_mm = mm;
 	preempt_disable();
 	update_mm(mm, tsk);
-	cpu_set(smp_processor_id(), mm->cpu_vm_mask);
+	cpumask_set_cpu(smp_processor_id(), mm_cpumask(mm));
 	preempt_enable();
 	task_unlock(tsk);
 	mmput(old_mm);