x86/pci: Use u64 instead of size_t in amd_bus.c

Prepare to enable it for 32bit.

-v2: remove not needed cast

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
LKML-Reference: <1265793639-15071-7-git-send-email-yinghai@kernel.org>
Acked-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>