usb: mtu3: clear dual mode of u3port when disable device

If not clear u3port's dual mode when disable device, the IP
will fail to enter sleep mode when suspend.

Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Link: https://lore.kernel.org/r/1595834101-13094-10-git-send-email-chunfeng.yun@mediatek.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>