ACPICA: Eliminate extra call to NsGetParentNode

Was called twice in the same function with the same parameter.
Alex Chiang.

Signed-off-by: Alex Chiang <achiang@hp.com>
Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Lin Ming <ming.m.lin@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>