perf probe: Don't use strerror if strlist__add failed

Since the strlist__add doesn't involves any IO, the failure reason must
be ENOMEM or EINVAL, moreover this is just a debug message, we don't
need to show the error string.

And also, if get_probe_trace_command_rawlist() returns NULL, it doesn't
mean the rawlist is empty, there is an error.  So caller must use
-ENOMEM for the error.
Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Naohiro Aota <naota@elisp.net>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20140814022230.3545.99254.stgit@kbuild-fedora.novalocalSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/probe-event.c

@@ -1881,7 +1881,7 @@ static struct strlist *get_probe_trace_command_rawlist(int fd)
 			p[idx] = '\0';
 		ret = strlist__add(sl, buf);
 		if (ret < 0) {
-			pr_debug("strlist__add failed: %s\n", strerror(-ret));
+			pr_debug("strlist__add failed (%d)\n", ret);
 			strlist__delete(sl);
 			return NULL;
 		}
@@ -1940,7 +1940,7 @@ static int __show_perf_probe_events(int fd, bool is_kprobe)
 
 	rawlist = get_probe_trace_command_rawlist(fd);
 	if (!rawlist)
-		return -ENOENT;
+		return -ENOMEM;
 
 	strlist__for_each(ent, rawlist) {
 		ret = parse_probe_trace_command(ent->s, &tev);
@@ -2007,6 +2007,8 @@ static struct strlist *get_probe_trace_event_names(int fd, bool include_group)
 
 	memset(&tev, 0, sizeof(tev));
 	rawlist = get_probe_trace_command_rawlist(fd);
+	if (!rawlist)
+		return NULL;
 	sl = strlist__new(true, NULL);
 	strlist__for_each(ent, rawlist) {
 		ret = parse_probe_trace_command(ent->s, &tev);