workqueue: fix opencoded cpumask_next_and_wrap() in wq_select_unbound_cpu()

The dedicated helper is more verbose and effective comparing to
cpumask_first() followed by cpumask_next().

Signed-off-by: Yury Norov [NVIDIA] <yury.norov@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

Author: YuryNorov

kernel/workqueue.c

@@ -2221,12 +2221,9 @@ static int wq_select_unbound_cpu(int cpu)
 	}
 
 	new_cpu = __this_cpu_read(wq_rr_cpu_last);
-	new_cpu = cpumask_next_and(new_cpu, wq_unbound_cpumask, cpu_online_mask);
-	if (unlikely(new_cpu >= nr_cpu_ids)) {
-		new_cpu = cpumask_first_and(wq_unbound_cpumask, cpu_online_mask);
-		if (unlikely(new_cpu >= nr_cpu_ids))
-			return cpu;
-	}
+	new_cpu = cpumask_next_and_wrap(new_cpu, wq_unbound_cpumask, cpu_online_mask);
+	if (unlikely(new_cpu >= nr_cpu_ids))
+		return cpu;
 	__this_cpu_write(wq_rr_cpu_last, new_cpu);
 
 	return new_cpu;