Internals: More const. No functional change intended.

src/V3Branch.cpp

@@ -40,7 +40,7 @@ private:
     // NODE STATE
     // Entire netlist:
     //  AstFTask::user1()       -> int.  Number of references
-    AstUser1InUse m_inuser1;
+    const AstUser1InUse m_inuser1;
 
     // STATE
     int m_likely = false;  // Excuses for branch likely taken