jack_load_test: fix parameter help

jack_get_time() returns microseconds, not seconds. See:

https://jackaudio.org/api/group__TimeFunctions.html#ga3b26460e62a56cf012e9075dcb1b6294

tools/load_test.c

@@ -26,7 +26,7 @@ show_usage (void)
 	fprintf (stderr, "\nUsage: %s [options]\n", my_name);
 	fprintf (stderr, "this is a test client, which just sleeps in its process_cb to simulate cpu load\n");
 	fprintf (stderr, "options:\n");
-	fprintf (stderr, "        -t, --timeout         Wait timeout in seconds\n");
+	fprintf (stderr, "        -t, --timeout         Wait timeout in microseconds\n");
 	fprintf (stderr, "        -h, --help            Display this help message\n");
 	fprintf (stderr, "        --version             Output version information and exit\n\n");
 	fprintf (stderr, "For more information see http://jackaudio.org/\n");