perf report: Fix -T/--threads option to work again

The commit 512ae1bd6acb ("perf tools: Consolidate management of default
sort orders") changed default value of the 'sort_order' variable to NULL
indicating that users don't set any sort keys on the command line.

However it missed to update a check in perf_evlist__tty_browse_hists()
so that 'perf report -T' cannot show the per-thread values after the
normal output. This patch fixes it to work again.

Note that the -T option only works on --stdio and neither --sort nor
--parent option was given.

Signed-off-by: Namhyung Kim <[e-mail]>
Cc: Andi Kleen <[e-mail]>
Cc: David Ahern <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Stephane Eranian <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/builtin-report.c

···
 		fprintf(stdout, "\n\n");
 	}
 
-	if (sort_order == default_sort_order &&
+	if (sort_order == NULL &&
 	    parent_pattern == default_parent_pattern) {
 		fprintf(stdout, "#\n# (%s)\n#\n", help);