[turbofan] Do not set node's mark to min on get

src/compiler/node.h

Index: src/compiler/node.h
diff --git a/src/compiler/node.h b/src/compiler/node.h
index dc6c5dc01c3ec88c1caea821970e341c411b4d27..06b6699c0beead376770d8c4426931bb12bc969b 100644
--- a/src/compiler/node.h
+++ b/src/compiler/node.h
@@ -294,7 +294,7 @@ class V8_EXPORT_PRIVATE Node final {
   void set_type(Type* type) { type_ = type; }
 
   // Only NodeMarkers should manipulate the marks on nodes.
-  Mark mark() { return mark_; }
+  Mark mark() const { return mark_; }
   void set_mark(Mark mark) { mark_ = mark; }
 
   inline bool has_inline_inputs() const {