usb: xhci-mtk: use ports count from xhci in xhci_mtk_sch_init()

Make use of ports count from xhci but not from ippc in
xhci_mtk_sch_init()

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