ITS: do not use NAN in helpers for new ROCm

fixes:
 /home/fschlepp/alice/sw/SOURCES/O2/dev_head/0/Detectors/ITSMFT/ITS/tracking/include/ITStracking/TrackHelpers.h:65:60: warning: use of NaN is undefined behavior due to the currently enabled floating-point options [-Wnan-infinity-disabled]
    65 |   float ca = NAN, sa = NAN, snp = NAN, q2pt = NAN, q2pt2 = NAN;
       |                                                            ^~~
 /opt/rocm-7.1.1/lib/llvm/lib/clang/20/include/float.h:174:16: note: expanded from macro 'NAN'
   174 | #  define NAN (__builtin_nanf(""))

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

Author: f3sch

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

@@ -62,7 +62,7 @@ GPUdi() o2::track::TrackParCov buildTrackSeed(const Cluster& cluster1,
                                               const float bz,
                                               const bool reverse = false)
 {
-  float ca = NAN, sa = NAN, snp = NAN, q2pt = NAN, q2pt2 = NAN;
+  float ca = constants::UnsetValue, sa = constants::UnsetValue, snp = constants::UnsetValue, q2pt = constants::UnsetValue, q2pt2 = constants::UnsetValue;
   o2::gpu::CAMath::SinCos(tf3.alphaTrackingFrame, sa, ca);
   const float sign = reverse ? -1.f : 1.f;
   const float x1 = (cluster1.xCoordinate * ca) + (cluster1.yCoordinate * sa);