usb: host: xhci: Remove unused 'addr_64' variable in xhci_hcd structure

Since the 'addr_64' variable as legacy is unused now, then remove it from
xhci_hcd structure.

Signed-off-by: Baolin Wang <baolin.wang@linaro.org>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>