cpu-hotplug: fix build on !CONFIG_SMP

fix build on !CONFIG_SMP.
Signed-off-by: Ingo Molnar <mingo@elte.hu>

include/linux/cpu.h

@@ -71,19 +71,25 @@ static inline void unregister_cpu_notifier(struct notifier_block *nb)
 
 int cpu_up(unsigned int cpu);
 
+extern void cpu_hotplug_init(void);
+
 #else
 
 static inline int register_cpu_notifier(struct notifier_block *nb)
 {
 	return 0;
 }
+
 static inline void unregister_cpu_notifier(struct notifier_block *nb)
 {
 }
 
+static inline void cpu_hotplug_init(void)
+{
+}
+
 #endif /* CONFIG_SMP */
 extern struct sysdev_class cpu_sysdev_class;
-extern void cpu_hotplug_init(void);
 extern void cpu_maps_update_begin(void);
 extern void cpu_maps_update_done(void);