Avoid direct use of QuasiAtomic by using Atomic.

Change-Id: I92d0f822cddb2085de7cbb4c44c3a429081892a2
diff --git a/runtime/jdwp/jdwp_main.cc b/runtime/jdwp/jdwp_main.cc
index 64e9f37..7795b7c 100644
--- a/runtime/jdwp/jdwp_main.cc
+++ b/runtime/jdwp/jdwp_main.cc
@@ -577,7 +577,7 @@
     return -1;
   }
 
-  int64_t last = QuasiAtomic::Read64(&last_activity_time_ms_);
+  int64_t last = last_activity_time_ms_.LoadSequentiallyConsistent();
 
   /* initializing or in the middle of something? */
   if (last == 0) {