utilities: Fix warnings about readUpdate enumeration comparisons

applications/utilities/mesh/manipulation/singleCellMesh/singleCellMesh.C

@@ -121,7 +121,7 @@ int main(int argc, char *argv[])
 
 
         // Check for new mesh
-        if (mesh.readUpdate() != polyMesh::UNCHANGED)
+        if (mesh.readUpdate() != fvMesh::UNCHANGED)
         {
             Info<< "Detected changed mesh. Recreating singleCell mesh." << endl;
             scMesh.clear(); // remove any registered objects

applications/utilities/postProcessing/graphics/PVReaders/vtkPVFoam/vtkPVFoam.C

@@ -147,7 +147,7 @@ int Foam::vtkPVFoam::setTime(int nRequest, const double requestTimes[])
             if
             (
                 meshPtr_->readUpdate(fvMesh::stitchType::nonGeometric)
-             != polyMesh::UNCHANGED
+             != fvMesh::UNCHANGED
             )
             {
                 meshChanged_ = true;

src/finiteVolume/fvMesh/fvMesh.C

@@ -813,9 +813,8 @@ Foam::fvMesh::readUpdateState Foam::fvMesh::readUpdate
         case polyMesh::POINTS_MOVED:
             return
                 stitcher_.valid()
-             && stitcher_->stitches()
              && stitch != stitchType::none
-             && state != polyMesh::UNCHANGED
+             && stitcher_->stitches()
               ? STITCHED
               : POINTS_MOVED;
         case polyMesh::TOPO_CHANGE:
@@ -823,6 +822,8 @@ Foam::fvMesh::readUpdateState Foam::fvMesh::readUpdate
         case polyMesh::TOPO_PATCH_CHANGE:
             return TOPO_PATCH_CHANGE;
     }
+
+    return UNCHANGED;
 }