Tidy up memory barriers.

Change-Id: I937ea93e6df1835ecfe2d4bb7d84c24fe7fc097b
diff --git a/compiler/driver/compiler_driver.cc b/compiler/driver/compiler_driver.cc
index 1124541..9cffb3c 100644
--- a/compiler/driver/compiler_driver.cc
+++ b/compiler/driver/compiler_driver.cc
@@ -1404,7 +1404,7 @@
   }
 
   size_t NextIndex() {
-    return index_.fetch_add(1);
+    return index_.FetchAndAdd(1);
   }
 
  private: