perf test event_update: Fix memory leak of unit

ASan reports a memory leak while running:

  # perf test "49: Synthesize attr update"

Caused by a string being duplicated but never freed.

This patch adds the missing free().

Note that evsel->unit is not deallocated together with evsel since it is
supposed to be a constant string.
Signed-off-by: Riccardo Mancini <rickyman7@gmail.com>
Fixes: a6e52817 ("perf tools: Add event_update event unit type")
Cc: Ian Rogers <irogers@google.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>
Link: http://lore.kernel.org/lkml/1fbc8158663fb0d4d5392e36bae564f6ad60be3c.1626343282.git.rickyman7@gmail.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/tests/event_update.c

@@ -88,6 +88,7 @@ int test__event_update(struct test *test __maybe_unused, int subtest __maybe_unu
 	struct evsel *evsel;
 	struct event_name tmp;
 	struct evlist *evlist = evlist__new_default();
+	char *unit = strdup("KRAVA");
 
 	TEST_ASSERT_VAL("failed to get evlist", evlist);
 
@@ -98,7 +99,7 @@ int test__event_update(struct test *test __maybe_unused, int subtest __maybe_unu
 
 	perf_evlist__id_add(&evlist->core, &evsel->core, 0, 0, 123);
 
-	evsel->unit = strdup("KRAVA");
+	evsel->unit = unit;
 
 	TEST_ASSERT_VAL("failed to synthesize attr update unit",
 			!perf_event__synthesize_event_update_unit(NULL, evsel, process_event_unit));
@@ -118,6 +119,7 @@ int test__event_update(struct test *test __maybe_unused, int subtest __maybe_unu
 	TEST_ASSERT_VAL("failed to synthesize attr update cpus",
 			!perf_event__synthesize_event_update_cpus(&tmp.tool, evsel, process_event_cpus));
 
+	free(unit);
 	evlist__delete(evlist);
 	return 0;
 }