tracing: Remove extra space at the end of hwlat_detector/mode

Space is printed after each mode value including the last one:
$ echo \"$(sudo cat /sys/kernel/tracing/hwlat_detector/mode)\"
"none [round-robin] per-cpu "

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Link: https://lore.kernel.org/linux-trace-kernel/20230825103432.7750-1-m.kobuk@ispras.ru

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Fixes: 8fa826b ("trace/hwlat: Implement the mode config option")
Signed-off-by: Mikhail Kobuk <m.kobuk@ispras.ru>
Reviewed-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Acked-by: Daniel Bristot de Oliveira <bristot@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

Author: Mikhail Kobuk

kernel/trace/trace_hwlat.c

@@ -635,7 +635,7 @@ static int s_mode_show(struct seq_file *s, void *v)
 	else
 		seq_printf(s, "%s", thread_mode_str[mode]);
 
-	if (mode != MODE_MAX)
+	if (mode < MODE_MAX - 1) /* if mode is any but last */
 		seq_puts(s, " ");
 
 	return 0;