ACPICA: Fix for Load operator

Fixed a problem with the Load operator where an exception was not
returned in the case where the table is already loaded.

http://www.acpica.org/bugzilla/show_bug.cgi?id=463

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>