perf pmu: Make pmu_formats_string to check return value of strbuf

Make pmu_formats_string() to check return value of strbuf APIs so that
it can detect errors in it.

Signed-off-by: Masami Hiramatsu <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Link: http://lkml.kernel.org/r/20160510054744.6158.37810.stgit@devbox
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/util/pmu.c

···
 static char *pmu_formats_string(struct list_head *formats)
 {
 	struct perf_pmu_format *format;
-	char *str;
-	struct strbuf buf;
+	char *str = NULL;
+	struct strbuf buf = STRBUF_INIT;
 	unsigned i = 0;
 
 	if (!formats)
 		return NULL;
 
-	strbuf_init(&buf, 0);
 	/* sysfs exported terms */
 	list_for_each_entry(format, formats, list)
-		strbuf_addf(&buf, i++ ? ",%s" : "%s",
-			    format->name);
+		if (strbuf_addf(&buf, i++ ? ",%s" : "%s", format->name) < 0)
+			goto error;
 
 	str = strbuf_detach(&buf, NULL);
+error:
 	strbuf_release(&buf);
 
 	return str;