usb: host: imx21: 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/1573541519-28488-3-git-send-email-chunfeng.yun@mediatek.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/host/imx21-dbg.c

@@ -419,7 +419,7 @@ static void create_debug_files(struct imx21 *imx21)
 {
 	struct dentry *root;
 
-	root = debugfs_create_dir(dev_name(imx21->dev), NULL);
+	root = debugfs_create_dir(dev_name(imx21->dev), usb_debug_root);
 	imx21->debug_root = root;
 
 	debugfs_create_file("status", S_IRUGO, root, imx21, &debug_status_fops);