ACPICA: Fix warning for 64-bit build

Fixes warning from exconfig.c on 64-bit build.

AK: This actually was fixed earlier in Linux, this just syncs with
AK: the version of the fix that went into the ACPCA codebase

Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Lin Ming <ming.m.lin@intel.com>
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>