Fix the sense of when mutexes are used for longs in atomic support.

Change-Id: Ice50519a511e98fdc2fe74cd9eb77c32872022b4
diff --git a/runtime/atomic.h b/runtime/atomic.h
index 6867fef..1f975dc 100644
--- a/runtime/atomic.h
+++ b/runtime/atomic.h
@@ -196,7 +196,7 @@
 
   // Does the architecture provide reasonable atomic long operations or do we fall back on mutexes?
   static bool LongAtomicsUseMutexes() {
-    return !kNeedSwapMutexes;
+    return kNeedSwapMutexes;
   }
 
   static void MembarLoadStore() {