ACPICA: Utilities: Cleanup style issue for bit clearing

ACPICA commit b49a0e1e26f3c61df7113f18f441c83739eb5514

It's reported in Linux community that change to utmath.c contains a style
problem:
 [.../utmath.c:137]: (style) Same expression on both sides of '^='.
 [.../utmath.c:174]: (style) Same expression on both sides of '^='.
This patch fixes this problem. ACPICA BZ 1422, reported by David Binderman,
fixed by Lv Zheng.

Link: https://github.com/acpica/acpica/commit/b49a0e1e
Link: https://bugs.acpica.org/show_bug.cgi?id=1422


Reported-by: David Binderman <dcb314@hotmail.com>
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
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>