generic-ipi: fix hotplug_cfd()

Use CONFIG_HOTPLUG_CPU, not CONFIG_CPU_HOTPLUG

When hot-unpluging a cpu, it will leak memory allocated at cpu hotplug,
but only if CPUMASK_OFFSTACK=y, which is default to n.

The bug was introduced by 8969a5ede0f9e17da4b943712429aef2c9bcd82b
("generic-ipi: remove kmalloc()").

Signed-off-by: Xiao Guangrong <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Jens Axboe <[e-mail]>
Cc: Nick Piggin <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Rusty Russell <[e-mail]>
Cc: <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

kernel/smp.c

···
 			return NOTIFY_BAD;
 		break;
 
-#ifdef CONFIG_CPU_HOTPLUG
+#ifdef CONFIG_HOTPLUG_CPU
 	case CPU_UP_CANCELED:
 	case CPU_UP_CANCELED_FROZEN: