ACPICA: Add a couple of casts to uthex.c

ACPICA commit 2ba5d3fdaa24d66d67694cbae6ec66971a7a67c1

Required in some environments.

Link: https://github.com/acpica/acpica/commit/2ba5d3fd


Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>