[PATCH] x86_64: Don't look up struct page pointer of physical address in iounmap

It could be in a memory hole not mapped in mem_map and that causes the hash
lookup to go off to nirvana.

Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>