usb: mtu3: fix uncontinuous SeqN issue after disable EP

Reset EP when disable it to reset data toggle for U2 EP, and
SeqN, flow control status etc for U3 EP, this can avoid
issue of uncontinuous SeqN

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