cpu/hotplug: Simplify access to percpu cpuhp_state

It is unnecessary to invoke per_cpu_ptr() everytime to access cpuhp_state.
Use the available pointer instead.

Signed-off-by: Yuan ZhaoXiong <yuanzhaoxiong@baidu.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Link: https://lore.kernel.org/r/1621776690-13264-1-git-send-email-yuanzhaoxiong@baidu.com

Author: Yuan ZhaoXiong

kernel/cpu.c

@@ -961,7 +961,7 @@ static int takedown_cpu(unsigned int cpu)
 	int err;
 
 	/* Park the smpboot threads */
-	kthread_park(per_cpu_ptr(&cpuhp_state, cpu)->thread);
+	kthread_park(st->thread);
 
 	/*
 	 * Prevent irq alloc/free while the dying cpu reorganizes the
@@ -977,7 +977,7 @@ static int takedown_cpu(unsigned int cpu)
 		/* CPU refused to die */
 		irq_unlock_sparse();
 		/* Unpark the hotplug thread so we can rollback there */
-		kthread_unpark(per_cpu_ptr(&cpuhp_state, cpu)->thread);
+		kthread_unpark(st->thread);
 		return err;
 	}
 	BUG_ON(cpu_online(cpu));