perf header: Fix bogus group name

When processing event group descriptor in perf file header, we reuse an
allocated group name but forgot to prevent it from freeing.

Reported-by: Stephane Eranian <[e-mail]>
Signed-off-by: Namhyung Kim <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Paul Mackerras <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/util/header.c

···
 		if (evsel->idx == (int) desc[i].leader_idx) {
 			evsel->leader = evsel;
 			/* {anon_group} is a dummy name */
-			if (strcmp(desc[i].name, "{anon_group}"))
+			if (strcmp(desc[i].name, "{anon_group}")) {
 				evsel->group_name = desc[i].name;
+				desc[i].name = NULL;
+			}
 			evsel->nr_members = desc[i].nr_members;
 
 			if (i >= nr_groups || nr > 0) {