Internals: More const. No functional change intended.

src/V3Slice.cpp

@@ -50,7 +50,7 @@ class SliceVisitor final : public AstNVisitor {
     //  AstNodeAssign::user1()      -> bool.  True if find is complete
     //  AstNodeUniop::user1()       -> bool.  True if find is complete
     //  AstArraySel::user1p()       -> AstVarRef. The VarRef that the final ArraySel points to
-    AstUser1InUse m_inuser1;
+    const AstUser1InUse m_inuser1;
 
     // STATE
     AstNode* m_assignp = nullptr;  // Assignment we are under