perf tools: Improve ambiguous option help message

Currently if an option name is ambiguous it only prints first two
matched option names but no help.  It'd be better it could show all
possible names and help messages too.

Before:
  $ perf report --show
    Error: Ambiguous option: show (could be --show-total-period or
                                            --show-ref-call-graph)
   Usage: perf report [<options>]

After:
  $ perf report --show
    Error: Ambiguous option: show (could be --show-total-period or
                                            --show-ref-call-graph)
   Usage: perf report [<options>]

      -n, --show-nr-samples
                              Show a column with the number of samples
          --showcpuutilization
                              Show sample percentage for different cpu modes
      -I, --show-info         Display extended information about perf.data file
          --show-total-period
                              Show a column with the sum of periods
          --show-ref-call-graph
                              Show callgraph from reference event
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1445701767-12731-1-git-send-email-namhyung@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/parse-options.c

@@ -770,24 +770,23 @@ int parse_options_usage(const char * const *usagestr,
 opt:
 	for (  ; opts->type != OPTION_END; opts++) {
 		if (short_opt) {
-			if (opts->short_name == *optstr)
+			if (opts->short_name == *optstr) {
+				print_option_help(opts, 0);
 				break;
+			}
 			continue;
 		}
 
 		if (opts->long_name == NULL)
 			continue;
 
-		if (!prefixcmp(optstr, opts->long_name))
-			break;
-		if (!prefixcmp(optstr, "no-") &&
-		    !prefixcmp(optstr + 3, opts->long_name))
-			break;
+		if (!prefixcmp(opts->long_name, optstr))
+			print_option_help(opts, 0);
+		if (!prefixcmp("no-", optstr) &&
+		    !prefixcmp(opts->long_name, optstr + 3))
+			print_option_help(opts, 0);
 	}
 
-	if (opts->type != OPTION_END)
-		print_option_help(opts, 0);
-
 	return PARSE_OPT_HELP;
 }