ACPICA: Fix a regression for deletion of Alias() objects.

Fixes a regression introduced by commit e23d9b829754 (ACPICA:
Namespace: Properly null terminate objects detached from a namespace
node)

In the case of Alias namespace nodes, the node simply points to the aliased
node via the Object field; thus we cannot assume that the object is an
operand object.

Fixes: e23d9b829754 (ACPICA: Namespace: Properly null terminate objects detached from a namespace node)
Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>