perf stat: Fix memory leak on error path

strdup() is used to deduplicate, ensure it isn't leaking an already
created string by freeing first.

Signed-off-by: Ian Rogers <[e-mail]>
Cc: Alexander Shishkin <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: John Garry <[e-mail]>
Cc: Mark Rutland <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Stephane Eranian <[e-mail]>
Link: http://lore.kernel.org/lkml/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/util/stat-shadow.c

···
 						"Add %s event to groups to get metric expression for %s\n",
 						metric_name,
 						counter->name);
+					free(printed);
 					printed = strdup(metric_name);
 				}
 				invalid = true;