usb: chipidea: debug: create debugfs directory under usb root

Move it's directory from the root of the debugfs filesystem into
the root of usb
Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Link: https://lore.kernel.org/r/1573541519-28488-2-git-send-email-chunfeng.yun@mediatek.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/chipidea/debug.c

@@ -342,7 +342,7 @@ DEFINE_SHOW_ATTRIBUTE(ci_registers);
  */
 void dbg_create_files(struct ci_hdrc *ci)
 {
-	ci->debugfs = debugfs_create_dir(dev_name(ci->dev), NULL);
+	ci->debugfs = debugfs_create_dir(dev_name(ci->dev), usb_debug_root);
 
 	debugfs_create_file("device", S_IRUGO, ci->debugfs, ci,
 			    &ci_device_fops);