Correctly find last visible usage in chain

bug: 158792096
Test: manual
Change-Id: I18bee272de79594103bc96253256fec6fc6d62cd

services/core/java/com/android/server/appop/DiscreteRegistry.java

@@ -542,7 +542,7 @@ final class DiscreteRegistry {
 
         private OpEvent getLastVisible() {
             // Search all nodes but the first one, which is the start node
-            for (int i = mChain.size() - 1; i > 0; i++) {
+            for (int i = mChain.size() - 1; i > 0; i--) {
                 OpEvent event = mChain.get(i);
                 if (!mExemptPkgs.contains(event.mPkgName)) {
                     return event;