clockevents: export clockevents_unbind_device instead of clockevents_unbind

It looks like clockevents_unbind is being exported by mistake as:
- it is static;
- it is not listed in include/linux/clockchips.h;
- EXPORT_SYMBOL_GPL(clockevents_unbind) follows clockevents_unbind_device()
  implementation.

I think clockevents_unbind_device should be exported instead. This is going to
be used to teardown Hyper-V clockevent devices on module unload.
Signed-off-by: NVitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: NK. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

kernel/time/clockevents.c

@@ -371,7 +371,7 @@ int clockevents_unbind_device(struct clock_event_device *ced, int cpu)
 	mutex_unlock(&clockevents_mutex);
 	return ret;
 }
-EXPORT_SYMBOL_GPL(clockevents_unbind);
+EXPORT_SYMBOL_GPL(clockevents_unbind_device);
 
 /**
  * clockevents_register_device - register a clock event device