usb: xhci-mtk: add a function to (un)load bandwidth info

Extract a function to load/unload bandwidth info, and remove
a dummy check of TT offset.

Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Link: https://lore.kernel.org/r/6fbc000756a4a4a7efbce651b785fee7561becb6.1615170625.git.chunfeng.yun@mediatek.com


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