perf probe: Accept the instance number of kretprobe event

Since the commit 6a13a0d7 ("ftrace/kprobe: Show the maxactive number
on kprobe_events") introduced to show the instance number of kretprobe
events, the length of the 1st format of the kprobe event will not 1, but
it can be longer.  This caused a parser error in perf-probe.

Skip the length check the 1st format of the kprobe event to accept this
instance number.

Without this fix:

  # perf probe -a vfs_read%return
  Added new event:
    probe:vfs_read__return (on vfs_read%return)

  You can now use it in all perf tools, such as:

  	perf record -e probe:vfs_read__return -aR sleep 1

  # perf probe -l
  Semantic error :Failed to parse event name: r16:probe/vfs_read__return
    Error: Failed to show event list.

And with this fixes:

  # perf probe -a vfs_read%return
  ...
  # perf probe -l
    probe:vfs_read__return (on vfs_read%return)

Fixes: 6a13a0d7 ("ftrace/kprobe: Show the maxactive number on kprobe_events")
Reported-by: Yuxuan Shui <yshuiv7@gmail.com>
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Tested-by: Yuxuan Shui <yshuiv7@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: stable@vger.kernel.org
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=207587
Link: http://lore.kernel.org/lkml/158877535215.26469.1113127926699134067.stgit@devnote2Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/probe-event.c

@@ -1765,8 +1765,7 @@ int parse_probe_trace_command(const char *cmd, struct probe_trace_event *tev)
 	fmt1_str = strtok_r(argv0_str, ":", &fmt);
 	fmt2_str = strtok_r(NULL, "/", &fmt);
 	fmt3_str = strtok_r(NULL, " \t", &fmt);
-	if (fmt1_str == NULL || strlen(fmt1_str) != 1 || fmt2_str == NULL
-	    || fmt3_str == NULL) {
+	if (fmt1_str == NULL || fmt2_str == NULL || fmt3_str == NULL) {
 		semantic_error("Failed to parse event name: %s\n", argv[0]);
 		ret = -EINVAL;
 		goto out;