Fix cpplinter warning in identified RAA task

Author: mpuccio

PWGLF/Tasks/Nuspex/identifiedraa.cxx

@@ -222,6 +222,7 @@ struct identifiedraaTask {
   template <std::size_t i, typename T>
   void fillHistogramsData(T const& tracks)
   {
+    static_assert(i < 6, "Index i out of bounds");
     for (auto& track : tracks) {
       if (std::abs(track.eta()) > 0.8) {
         continue;
@@ -235,10 +236,8 @@ struct identifiedraaTask {
           continue;
         }
       }
-      float mass;
-      if constexpr ((i == 0) || (i == 1)) {
-        mass = 0.13957; // pion mass
-      } else if constexpr ((i == 2) || (i == 3)) {
+      float mass{0.13957};
+      if constexpr ((i == 2) || (i == 3)) {
         mass = 0.49367; // kaon mass
       } else if constexpr ((i == 4) || (i == 5)) {
         mass = 0.93827; // proton mass