tests: store XGL_GPU_MEMORYs in XglMemoryRefManager

XGL_GPU_MEMORY is already a pointer.
diff --git a/tests/xglrenderframework.h b/tests/xglrenderframework.h
index 4818626..9851bb9 100644
--- a/tests/xglrenderframework.h
+++ b/tests/xglrenderframework.h
@@ -291,7 +291,7 @@
 
 protected:
     int m_numRefs;
-    vector<XGL_GPU_MEMORY*> m_bufferObjs;
+    vector<XGL_GPU_MEMORY> m_bufferObjs;
 
 };