Revert "usb: mtu3: fix up undefined reference to usb_debug_root"

It's not needed after [1] is applied, because usb_debug_root is created
by usb common core but not usbcore now.

[1] 812086d ("USB: move usb debugfs directory creation to the usb common core")

Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/mtu3/mtu3_debugfs.c

@@ -528,7 +528,8 @@ void ssusb_dr_debugfs_init(struct ssusb_mtk *ssusb)
 
 void ssusb_debugfs_create_root(struct ssusb_mtk *ssusb)
 {
-	ssusb->dbgfs_root = debugfs_create_dir(dev_name(ssusb->dev), NULL);
+	ssusb->dbgfs_root =
+		debugfs_create_dir(dev_name(ssusb->dev), usb_debug_root);
 }
 
 void ssusb_debugfs_remove_root(struct ssusb_mtk *ssusb)