build: Fix clang errors

Change-Id: I0f8a9687e623c9da5275adc6dd69919368b1a627
diff --git a/layers/synchronization_validation.cpp b/layers/synchronization_validation.cpp
index 096c342..5b0460d 100644
--- a/layers/synchronization_validation.cpp
+++ b/layers/synchronization_validation.cpp
@@ -5099,7 +5099,7 @@
     assert(context);
     if (!context) return skip;
     // Validate Image Layout transitions
-    for (const auto image_barrier : image_memory_barriers_) {
+    for (const auto &image_barrier : image_memory_barriers_) {
         if (image_barrier.new_layout == image_barrier.old_layout) continue;  // Only interested in layout transitions at this point.
         const auto *image_state = image_barrier.image.get();
         if (!image_state) continue;