ACPICA: Macros: remove pointer math on a null pointer

ACPICA commit 02bbca5070e42d298c9b824300aa0eb8a082d797

Causes warnings on some compilers and/or tools.
Changed ACPI_TO_POINTER to use ACPI_CAST_PTR instead of using
arithmetic.

Link: https://github.com/acpica/acpica/commit/02bbca50


Reported-by: Qian Cai <cai@lca.pw>
Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Erik Schmauss <erik.schmauss@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>