Fix iteration over sub benchmarks in perf.py

Change-Id: I50e6539da39e03c65d1f7a965c2492ea7a3903fb

tools/perf.py

diff --git a/tools/perf.py b/tools/perf.py
index 8261605..0a7ba98 100755
--- a/tools/perf.py
+++ b/tools/perf.py
@@ -292,7 +292,7 @@
 
                 # Merge results and write output.
                 if sub_benchmarks_for_target:
-                    for sub_benchmark in sub_benchmarks:
+                    for sub_benchmark in sub_benchmarks_for_target:
                         ArchiveBenchmarkResult(
                             benchmark + sub_benchmark, target,
                             benchmark_result_json_files[sub_benchmark], options,