sparc: convert old cpumask API into new one

Adapt new API. Almost change is trivial, most important change are to
remove following like =operator.

 cpumask_t cpu_mask = *mm_cpumask(mm);
 cpus_allowed = current->cpus_allowed;

Because cpumask_var_t is =operator unsafe. These usage might prevent
kernel core improvement.

No functional change.

Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>