[PATCH] memhotplug: register_ and unregister_memory_notifier should be global

Both register_memory_notifer and unregister_memory_notifier are global and
declared so in linux/memory.h.  Update the HOTPLUG specific definitions to
match.  This fixes a compile warning when HOTPLUG is enabled.

Signed-off-by: Andy Whitcroft <apw@shadowen.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>