usb: mtu3: fix transfer error of USB3 Gen2 isoc

To support USB3 Gen2 ISOC, the registers of TXCSR1 and RXCSR1
are adjusted to support greater maxpkt and mult value, this
patch fix this issue

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