usb: xhci: fix config fail of FS hub behind a HS hub with MTT

if a full speed hub connects to a high speed hub which
supports MTT, the MTT field of its slot context will be set
to 1 when xHCI driver setups an xHCI virtual device in
xhci_setup_addressable_virt_dev(); once usb core fetch its
hub descriptor, and need to update the xHC's internal data
structures for the device, the HUB field of its slot context
will be set to 1 too, meanwhile MTT is also set before,
this will cause configure endpoint command fail, so in the
case, we should clear MTT to 0 for full speed hub according
to section 6.2.2

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