ITS: get cluster index only once

Signed-off-by: Felix Schlepper <felix.schlepper@cern.ch>

Author: f3sch

Detectors/ITSMFT/ITS/tracking/include/ITStracking/TrackHelpers.h

@@ -167,11 +167,12 @@ GPUdi() bool fitTrack(TrackITSInternal<NLayers>& trk,
                       o2::track::TrackPar* linRef = nullptr)
 {
   for (int iLayer{start}; iLayer != end; iLayer += step) {
-    if (trk.getClusterIndex(iLayer) == constants::UnusedIndex) {
+    const int clsIdx = trk.getClusterIndex(iLayer);
+    if (clsIdx == constants::UnusedIndex) {
       continue;
     }
 
-    const TrackingFrameInfo& trackingHit = ctx.tfInfos[iLayer][trk.getClusterIndex(iLayer)];
+    const TrackingFrameInfo& trackingHit = ctx.tfInfos[iLayer][clsIdx];
     if (linRef) {
       if (!param.o2::track::TrackParCovF::rotate(trackingHit.alphaTrackingFrame, *linRef, ctx.bz)) {
         return false;