Update donate_priority to only attempt to sort position of the donee that isn't waiting for a lock

src/threads/synch.c

@@ -214,12 +214,17 @@ donate_priority (struct thread *donor, struct thread *donee) {
       /* Also stop propagation of donation once a donee is reached with
          no donees of its own (sink node in WFG). */
       if (donee->waiting_lock == NULL)
-        donee = NULL;
+        {
+
+          /* Only the sink node of the WFG isn't waiting for a lock and
+             could be on the ready list. Thus, as its priority changed,
+             it must be reinserted into the list. */
+          ready_list_reinsert (donee);
+          donee = NULL;
+        }
       else
         donee = donee->waiting_lock->holder;
     }
-
-  ready_list_reorder ();
 }
 
 /* Acquires LOCK, sleeping until it becomes available if