ACPICA: Fix access width for reset vector

Section 4.7.3.6 of the ACPI specification requires that the register width
of the reset vector be 8 bits. Windows simply hardcodes the access to be
a byte and ignores the width provided in the FADT, so make sure that we
do the same.

Signed-off-by: Matthew Garrett <mjg@redhat.com>
Signed-off-by: Len Brown <len.brown@intel.com>