fvModels: Prevent ambiguity when using the index operator

fvModels should operate primarily like a list of fvModel-s, so the index
operator of relevance is the one from its list base class. This has been
made explicit to prevent ambiguity associated with the same operator in
the dictionary base class.

src/finiteVolume/cfdTools/general/fvModels/fvModels.H

@@ -263,6 +263,9 @@ public:
 
     // Member Operators
 
+        //- Inherit the PtrListDictionary index operators
+        using PtrListDictionary<fvModel>::operator[];
+
         //- Disallow default bitwise assignment
         void operator=(const fvModels&) = delete;