opal_lifo: fix potential race condition when using 128-bit atomics

On x86_64 reading a 128-bit value requires multiple instructions.
Under some conditions if the counted pointer counter is read before
the item pointer the fifo can be left in an inconsistent state. This
commit forces the read of the counter to always be read first.

The fifo does not appear to suffer from the same race.

opal/class/opal_lifo.h

@@ -122,7 +122,6 @@ static inline opal_list_item_t *opal_lifo_push_atomic (opal_lifo_t *lifo,
 
         /* to protect against ABA issues it is sufficient to only update the counter in pop */
         if (opal_atomic_cmpset_ptr (&lifo->opal_lifo_head.data.item, next, item)) {
-            opal_atomic_wmb ();
             return next;
         }
         /* DO some kind of pause to release the bus */
@@ -139,10 +138,9 @@ static inline opal_list_item_t *opal_lifo_pop_atomic (opal_lifo_t* lifo)
     do {
         opal_counted_pointer_t old_head;
 
+        old_head.data.counter = lifo->opal_lifo_head.data.counter;
         opal_atomic_rmb ();
-
+        item = old_head.data.item = lifo->opal_lifo_head.data.item;
-        old_head.value = lifo->opal_lifo_head.value;
-        item = old_head.data.item;
 
         if (item == &lifo->opal_lifo_ghost) {
             return NULL;