arch/x86/mm/numa.c: fix array index overflow when synchronizing nid to memblock.reserved.

The following path will cause array out of bound.

memblock_add_region() will always set nid in memblock.reserved to
MAX_NUMNODES.  In numa_register_memblks(), after we set all nid to
correct valus in memblock.reserved, we called setup_node_data(), and
used memblock_alloc_nid() to allocate memory, with nid set to
MAX_NUMNODES.

The nodemask_t type can be seen as a bit array.  And the index is 0 ~
MAX_NUMNODES-1.

After that, when we call node_set() in numa_clear_kernel_node_hotplug(),
the nodemask_t got an index of value MAX_NUMNODES, which is out of [0 ~
MAX_NUMNODES-1].

See below:

numa_init()
 |---> numa_register_memblks()
 |      |---> memblock_set_node(memory)		set correct nid in memblock.memory
 |      |---> memblock_set_node(reserved)	set correct nid in memblock.reserved
 |      |......
 |      |---> setup_node_data()
 |             |---> memblock_alloc_nid()	here, nid is set to MAX_NUMNODES (1024)
 |......
 |---> numa_clear_kernel_node_hotplug()
        |---> node_set()			here, we have an index 1024, and overflowed

This patch moves nid setting to numa_clear_kernel_node_hotplug() to fix
this problem.

Reported-by: Dave Jones <davej@redhat.com>
Signed-off-by: Tang Chen <tangchen@cn.fujitsu.com>
Tested-by: Gu Zheng <guz.fnst@cn.fujitsu.com>
Reported-by: Dave Jones <davej@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Tested-by: Dave Jones <davej@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>