ACPICA: Fix for invalid large array index on 64-bit systems

This problem was introduced in 20080514 as a result of the
elimination of the acpi_native_uint type. Code uses a negative
array index, which should be eliminated.

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