ACPICA: Fix for access to deleted object <regression>

Fixes problem introduced in 20080123, with fix for Unload operator.
Parse tree object can be already deleted; must use the opcode
within the WalkState.

ACPI: kmemcheck: Caught 16-bit read from freed memory
http://bugzilla.kernel.org/show_bug.cgi?id=10669

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

drivers/acpi/parser/psargs.c

@@ -268,7 +268,7 @@ acpi_ps_get_next_namepath(struct acpi_walk_state *walk_state,
 	 */
 	if (ACPI_SUCCESS(status) &&
 	    possible_method_call && (node->type == ACPI_TYPE_METHOD)) {
-		if (walk_state->op->common.aml_opcode == AML_UNLOAD_OP) {
+		if (walk_state->opcode == AML_UNLOAD_OP) {
 			/*
 			 * acpi_ps_get_next_namestring has increased the AML pointer,
 			 * so we need to restore the saved AML pointer for method call.
@@ -691,7 +691,7 @@ acpi_ps_get_next_arg(struct acpi_walk_state *walk_state,
 
 			/* To support super_name arg of Unload */
 
-			if (walk_state->op->common.aml_opcode == AML_UNLOAD_OP) {
+			if (walk_state->opcode == AML_UNLOAD_OP) {
 				status =
 				    acpi_ps_get_next_namepath(walk_state,
 							      parser_state, arg,