[doc] Fix some fluid density ogs_file_param's.

Documentation/ProjectFile/material/fluid/density/t_value.md

+\ogs_missing_documentation

MaterialLib/Fluid/Density/createFluidDensityModel.cpp

@@ -74,21 +74,17 @@ std::unique_ptr<FluidProperty> createFluidDensityModel(
     if (type == "Constant")
     {
         return std::unique_ptr<FluidProperty>(new ConstantFluidProperty(
-            //! \ogs_file_param{material__fluid__density__Constant_value}
+            //! \ogs_file_param{material__fluid__density__value}
             config.getConfigParameter<double>("value")));
     }
-    //! \ogs_file_param{material__fluid__density__LiquidDensity}
     else if (type == "LiquidDensity")
         return createLiquidDensity(config);
-
-    //! \ogs_file_param{material__fluid__density__TemperatureDependent}
     else if (type == "TemperatureDependent")
         return createLinearTemperatureDependentDensity(config);
-    //! \ogs_file_param{material__fluid__density__IdealGasLaw}
     else if (type == "IdealGasLaw")
     {
-        //! \ogs_file_param{material__fluid__density__IdealGasLaw__molar_mass}
         return std::unique_ptr<FluidProperty>(
+            //! \ogs_file_param{material__fluid__density__IdealGasLaw__molar_mass}
             new IdealGasLaw(config.getConfigParameter<double>("molar_mass")));
     }
     else

MaterialLib/Fluid/Viscosity/createViscosityModel.cpp

@@ -80,7 +80,7 @@ std::unique_ptr<FluidProperty> createViscosityModel(
     {
         INFO("Using Vogels model, which gives viscosity in SI unit, Pa s");
         auto const fluid_type =
-            //! \ogs_file_param{material__fluid__viscosity__Vogels__fluid_type}
+            //! \ogs_file_param{material__fluid__viscosity__Vogels__liquid_type}
             config.getConfigParameter<std::string>("liquid_type");
         if (fluid_type == "Water")
         {