[turbofan] fix block mapping in code comments

src/compiler/instruction.h

Index: src/compiler/instruction.h
diff --git a/src/compiler/instruction.h b/src/compiler/instruction.h
index 72ea0433d59d536491a7d73f524908bd55e4df5d..fc4778f8949f9be318ead5e53d707cae25bae169 100644
--- a/src/compiler/instruction.h
+++ b/src/compiler/instruction.h
@@ -598,6 +598,7 @@ class BlockStartInstruction FINAL : public GapInstruction {
  public:
   Label* label() { return &label_; }
   BasicBlock::RpoNumber rpo_number() const { return rpo_number_; }
+  BasicBlock::Id id() const { return id_; }
 
   static BlockStartInstruction* New(Zone* zone, BasicBlock* block) {
     void* buffer = zone->New(sizeof(BlockStartInstruction));
@@ -612,8 +613,10 @@ class BlockStartInstruction FINAL : public GapInstruction {
  private:
   explicit BlockStartInstruction(BasicBlock* block)
       : GapInstruction(kBlockStartInstruction),
+        id_(block->id()),
         rpo_number_(block->GetRpoNumber()) {}
 
+  BasicBlock::Id id_;
   BasicBlock::RpoNumber rpo_number_;
   Label label_;
 };