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 <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Naohiro Aota <[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/probe-event.c

···
 			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;
 		}
···
 
 	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);
···
 
 	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);