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/nodes.h b/compiler/optimizing/nodes.h
index 4670b3f..fedad0c 100644
--- a/compiler/optimizing/nodes.h
+++ b/compiler/optimizing/nodes.h
@@ -2934,7 +2934,7 @@
   size_t ComputeHashCode() const override { return 0; }
 
   // The null constant representation is a 0-bit pattern.
-  virtual bool IsZeroBitPattern() const { return true; }
+  bool IsZeroBitPattern() const override { return true; }
 
   DECLARE_INSTRUCTION(NullConstant);
 
@@ -6316,7 +6316,7 @@
 
   bool CanBeMoved() const override { return true; }
 
-  bool InstructionDataEquals(const HInstruction* other) const;
+  bool InstructionDataEquals(const HInstruction* other) const override;
 
   size_t ComputeHashCode() const override { return type_index_.index_; }