Fix doing preroll for postroll

Test: ./build/make/tools/perf/benchmarks
Change-Id: Ib64ddd53ea9234dc2934fd6dea988add02729d29
diff --git a/tools/perf/benchmarks b/tools/perf/benchmarks
index acc53bb..61bf888 100755
--- a/tools/perf/benchmarks
+++ b/tools/perf/benchmarks
@@ -302,7 +302,7 @@
                 self._dist(utils.get_dist_dir())
             else:
                 # Postroll builds
-                for i in range(benchmark.preroll):
+                for i in range(benchmark.postroll):
                     ns = self._run_build(lunch, benchmark_log_dir.joinpath(f"post_{i}"),
                                          benchmark.modules)
                     report.postroll_duration_ns.append(ns)