fix this small typo u3_ports_disabed => u3_ports_disabled

Fixes: 55ba6e9e (usb: xhci-mtk: support option to disable usb3 ports)
Signed-off-by: Frank Wunderlich <frank-w@public-files.de>
Reviewed-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Link: https://lore.kernel.org/r/20200808124906.89976-1-linux@fw-web.deSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>