usb: xhci-mtk: fix bpkts value of LS/HS periodic eps not behind TT

when a LS or FS device doesn't connect though a HS hub,
the @bPkts field of its periodic endpoint context should
be set to 1.

Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>