sched: use group_first_cpu() instead of cpumask_first(sched_group_cpus())

Impact: cleanup

This patch changes cpumask_first(sched_group_cpus()) to group_first_cpu()
for maintainability.

Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/sched.c b/kernel/sched.c
index 92b4b56..7601cee 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -7995,7 +7995,7 @@
 			struct sched_domain *sd;
 
 			sd = &per_cpu(phys_domains, j).sd;
-			if (j != cpumask_first(sched_group_cpus(sd->groups))) {
+			if (j != group_first_cpu(sd->groups)) {
 				/*
 				 * Only add "power" once for each
 				 * physical package.
@@ -8073,7 +8073,7 @@
 
 	WARN_ON(!sd || !sd->groups);
 
-	if (cpu != cpumask_first(sched_group_cpus(sd->groups)))
+	if (cpu != group_first_cpu(sd->groups))
 		return;
 
 	child = sd->child;