layers: Fix object_tracker warnings in Android and Win32 builds

Change-Id: If937c4c5aca0dc274aa67a9b52b99909723f082c
diff --git a/tests/layer_validation_tests.cpp b/tests/layer_validation_tests.cpp
index 46cb414..3f8bda6 100644
--- a/tests/layer_validation_tests.cpp
+++ b/tests/layer_validation_tests.cpp
@@ -667,7 +667,7 @@
                       (void **)&pData);
     ASSERT_VK_SUCCESS(err);
 
-    memset(pData, 0xCADECADE, mem_reqs.size);
+    memset(pData, 0xCADECADE, static_cast<size_t>(mem_reqs.size));
 
     vkUnmapMemory(m_device->device(), mem);