ACPICA: actbl2: Replace 1-element arrays with flexible arrays

ACPICA commit 44f1af0664599e87bebc3a1260692baa27b2f264

Similar to "Replace one-element array with flexible-array", replace the
1-element array with a proper flexible array member as defined by C99.

This allows the code to operate without tripping compile-time and run-
time bounds checkers (e.g. via __builtin_object_size(), -fsanitize=bounds,
and/or -fstrict-flex-arrays=3).

The sizeof() uses with struct acpi_nfit_flush_address and struct
acpi_nfit_smbios have been adjusted to drop the open-coded subtraction
of the trailing single element. The result is no binary differences in
.text nor .data sections.

Link: https://github.com/acpica/acpica/commit/44f1af06


Signed-off-by: Bob Moore <robert.moore@intel.com>
Co-developed-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>