xhci: rename faked_port_index to hcd_portnum

hcd_portnum is a better desctiption than faked_port_index, and
is in line with the name the port structure uses.

No functional changes

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