memory hotplug x86_64: fix section mismatch in init_memory_mapping()

Changes __meminit to __init_refok.

WARNING: vmlinux.o(.text+0x1d07c): Section mismatch: reference to
.init.text:find_e820_area (between 'init_memory_mapping' and 'arch_add_memory')
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/x86/mm/init_64.c

@@ -345,7 +345,7 @@ static void __init find_early_table_space(unsigned long end)
 /* Setup the direct mapping of the physical memory at PAGE_OFFSET.
    This runs before bootmem is initialized and gets pages directly from the 
    physical memory. To access them they are temporarily mapped. */
-void __meminit init_memory_mapping(unsigned long start, unsigned long end)
+void __init_refok init_memory_mapping(unsigned long start, unsigned long end)
 { 
 	unsigned long next;