xhci: remove unused parameter 'xhci' in function xhci_handshake().

Parameter 'xhci' is no longer be used in function xhci_handshake(),
just remove it.

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