Modernise code to use override specifier

Generated by clang-tidy, with IgnoreDestructors option enabled.

Test: m checkbuild
Bug: 116509795
Change-Id: I5dafa10c2cf605165581b8cf7dd2633ed101ed65
diff --git a/compiler/optimizing/scheduler_arm.h b/compiler/optimizing/scheduler_arm.h
index 875593b..4c7a3bb 100644
--- a/compiler/optimizing/scheduler_arm.h
+++ b/compiler/optimizing/scheduler_arm.h
@@ -55,7 +55,7 @@
       : codegen_(down_cast<CodeGeneratorARMType*>(codegen)) {}
 
   // Default visitor for instructions not handled specifically below.
-  void VisitInstruction(HInstruction* ATTRIBUTE_UNUSED) {
+  void VisitInstruction(HInstruction* ATTRIBUTE_UNUSED) override {
     last_visited_latency_ = kArmIntegerOpLatency;
   }