ACPICA: Fixed a problem with CopyObject used in conjunction with the Index operator

The reference was incorrectly dereferenced before the copy. The
reference is now correctly copied.

http://bugzilla.kernel.org/show_bug.cgi?id=5391



Signed-off-by: Lin Ming <ming.m.lin@intel.com>
Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Alexey Starikovskiy <astarikovskiy@suse.de>
Signed-off-by: Len Brown <len.brown@intel.com>