Parenting: fix return value when parenting object to itself

Ensure parenting an object to itself is seen as error, by returning
`false`.

This error was introduced as part of a supposed-to-be-non-functional
cleanup rBb8d4a2aff8069dd7d6fb91ad0d9427eed489b68f.

source/blender/editors/object/object_relations.c

@@ -696,7 +696,7 @@ bool ED_object_parent_set(ReportList *reports,
   /* Preconditions. */
   if (ob == par) {
     /* Parenting an object to itself is impossible. */
-    return true;
+    return false;
   }
 
   if (BKE_object_parent_loop_check(par, ob)) {