x86: memtest: remove 64-bit division

Using gcc 3.3.5 a "make allmodconfig" + "CONFIG_KVM=n"
triggers a build error:

 arch/x86/mm/built-in.o(.init.text+0x43f7): In function `__change_page_attr':
 arch/x86/mm/pageattr.c:114: undefined reference to `__udivdi3'
 make: *** [.tmp_vmlinux1] Error 1

The culprit turned out to be a division in arch/x86/mm/memtest.c
For more info see this thread:

  http://marc.info/?l=linux-kernel&m=124416232620683

The patch entirely removes the division that caused the build
error.

[ Impact: build fix with certain GCC versions ]

Reported-by: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Signed-off-by: Andreas Herrmann <andreas.herrmann3@amd.com>
Cc: Yinghai Lu <yinghai@kernel.org>
Cc: xiyou.wangcong@gmail.com
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: <stable@kernel.org>
LKML-Reference: <20090608170939.GB12431@alberich.amd.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>