perf test: Fix msan uninitialized use.

Ensure 'st' is initialized before an error branch is taken.
Fixes test "67: Parse and process metrics" with LLVM msan:

  ==6757==WARNING: MemorySanitizer: use-of-uninitialized-value
    #0 0x5570edae947d in rblist__exit tools/perf/util/rblist.c:114:2
    #1 0x5570edb1c6e8 in runtime_stat__exit tools/perf/util/stat-shadow.c:141:2
    #2 0x5570ed92cfae in __compute_metric tools/perf/tests/parse-metric.c:187:2
    #3 0x5570ed92cb74 in compute_metric tools/perf/tests/parse-metric.c:196:9
    #4 0x5570ed92c6d8 in test_recursion_fail tools/perf/tests/parse-metric.c:318:2
    #5 0x5570ed92b8c8 in test__parse_metric tools/perf/tests/parse-metric.c:356:2
    #6 0x5570ed8de8c1 in run_test tools/perf/tests/builtin-test.c:410:9
    #7 0x5570ed8ddadf in test_and_print tools/perf/tests/builtin-test.c:440:9
    #8 0x5570ed8dca04 in __cmd_test tools/perf/tests/builtin-test.c:661:4
    #9 0x5570ed8dbc07 in cmd_test tools/perf/tests/builtin-test.c:807:9
    #10 0x5570ed7326cc in run_builtin tools/perf/perf.c:313:11
    #11 0x5570ed731639 in handle_internal_command tools/perf/perf.c:365:8
    #12 0x5570ed7323cd in run_argv tools/perf/perf.c:409:2
    #13 0x5570ed731076 in main tools/perf/perf.c:539:3

Fixes: commit f5a56570 ("perf test: Fix memory leaks in parse-metric test")
Signed-off-by: Ian Rogers <irogers@google.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: clang-built-linux@googlegroups.com
Link: http://lore.kernel.org/lkml/20200923210655.4143682-1-irogers@google.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/tests/parse-metric.c

@@ -157,6 +157,7 @@ static int __compute_metric(const char *name, struct value *vals,
 	}
 
 	perf_evlist__set_maps(&evlist->core, cpus, NULL);
+	runtime_stat__init(&st);
 
 	/* Parse the metric into metric_events list. */
 	err = metricgroup__parse_groups_test(evlist, &map, name,
@@ -170,7 +171,6 @@ static int __compute_metric(const char *name, struct value *vals,
 		goto out;
 
 	/* Load the runtime stats with given numbers for events. */
-	runtime_stat__init(&st);
 	load_runtime_stat(&st, evlist, vals);
 
 	/* And execute the metric */