unityLewisFourier,unityLewisEddyDiffusivity: Changed the specie diffusivity to be based on the enthalpy diffusivity

such that the Lewis number is unity with respect to enthalpy even when solving
for internal energy providing more consistent behaviour between the energy
choices.

src/ThermophysicalTransportModels/laminar/unityLewisFourier/unityLewisFourier.H

@@ -113,7 +113,7 @@ public:
             return volScalarField::New
             (
                 "DEff",
-                this->alphaEff()
+                this->thermo().alpha()
             );
         }
 
@@ -125,7 +125,7 @@ public:
             const label patchi
         ) const
         {
-            return this->alphaEff(patchi);
+            return this->thermo().alpha(patchi);
         }
 
         //- Return the heat flux [W/m^2]

src/ThermophysicalTransportModels/turbulence/unityLewisEddyDiffusivity/unityLewisEddyDiffusivity.H

@@ -185,7 +185,7 @@ public:
             return volScalarField::New
             (
                 "DEff",
-                alphaEff()
+                this->thermo().alpha() + alphat()
             );
         }
 
@@ -197,7 +197,7 @@ public:
             const label patchi
         ) const
         {
-            return alphaEff(patchi);
+            return this->thermo().alpha(patchi) + alphat(patchi);
         }
 
         //- Return the heat flux [W/m^2]