Fix warnings in hwiu test app

So it's easier to see warnings about actual
problems with new changes.

Change-Id: I992711bf12bb25fbfd87fcab15993d5c5f66f46c
diff --git a/libs/hwui/tests/main.cpp b/libs/hwui/tests/main.cpp
index 2d99e9f..64ee5f6 100644
--- a/libs/hwui/tests/main.cpp
+++ b/libs/hwui/tests/main.cpp
@@ -111,7 +111,7 @@
 
     for (int i = 0; i < 150; i++) {
         ATRACE_NAME("UI-Draw Frame");
-        for (int ci = 0; ci < cards.size(); ci++) {
+        for (size_t ci = 0; ci < cards.size(); ci++) {
             cards[ci]->mutateStagingProperties().setTranslationX(i);
             cards[ci]->mutateStagingProperties().setTranslationY(i);
             cards[ci]->setPropertyFieldsDirty(RenderNode::X | RenderNode::Y);