[FIFO] keep perf metric dict keys consistent in C++ fifo sim

src/finn/qnn-data/cpp/verilator_fifosim.cpp

@@ -152,8 +152,9 @@ int main(int argc, char *argv[]) {
     results_file.open("results.txt", ios::out | ios::trunc);
     results_file << "N_IN_TXNS" << "\t" << n_in_txns << endl;
     results_file << "N_OUT_TXNS" << "\t" << n_out_txns << endl;
-    results_file << "N_CYCLES" << "\t" << iters << endl;
-    results_file << "LATENCY" << "\t" << latency << endl;
+    results_file << "cycles" << "\t" << iters << endl;
+    results_file << "N" << "\t" << n_inputs << endl;
+    results_file << "latency_cycles" << "\t" << latency << endl;
 @FIFO_DEPTH_LOGGING@
     results_file.close();