Refactor lock release to follow PintOS indent style and use list functoins, w/ T

src/threads/synch.c

@@ -318,15 +318,8 @@ lock_release (struct lock *lock)
      released, transfer the remaining orphaned donors to its donor list. */
   if (max_donor != NULL)
     {
-    tail = list_tail (&orphan_list);
-    e = list_begin (&orphan_list);
-    while (e != tail)
-      {
-        struct list_elem *next = list_next (e);
-        list_push_back (&max_donor->donors_list, e);
-
-        e = next;
-      }
+      while (!list_empty (&orphan_list))
+        list_push_back (&max_donor->donors_list, list_pop_front (&orphan_list));
     }
 
   /* Removal of donors to this thread may change its effective priority,