IB/qib: Reset packet list after freeing

Reset the list pointers after freeing the SDMA packet list.  This is
done to any potential double-free cases.

Signed-off-by: Mike Marciniszyn <mike.marciniszyn@qlogic.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>

drivers/infiniband/hw/qib/qib_user_sdma.c

@@ -382,6 +382,7 @@ static void qib_user_sdma_free_pkt_list(struct device *dev,
 
 		kmem_cache_free(pq->pkt_slab, pkt);
 	}
+	INIT_LIST_HEAD(list);
 }
 
 /*