usb: dwc2: create debugfs directory under usb root

Now the USB gadget subsystem can use the USB debugfs root directory,
so move dwc2'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/1573541519-28488-7-git-send-email-chunfeng.yun@mediatek.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Chunfeng Yun

drivers/usb/dwc2/debugfs.c

@@ -770,7 +770,7 @@ int dwc2_debugfs_init(struct dwc2_hsotg *hsotg)
 	int			ret;
 	struct dentry		*root;
 
-	root = debugfs_create_dir(dev_name(hsotg->dev), NULL);
+	root = debugfs_create_dir(dev_name(hsotg->dev), usb_debug_root);
 	hsotg->debug_root = root;
 
 	debugfs_create_file("params", 0444, root, hsotg, &params_fops);