greybus: es2: Send cport-id in wValue field to usb_control_msg()

wIndex field has a special meaning, as that can be used by the core to
index into the possible USB interfaces. And that specifically broke with
gbsim, as it has a single USB interface.

Other similar requests (REQUEST_LATENCY_TAG_{EN|DIS}) are already using
wValue field for passing cport-id.

Fix cport_reset() by sending the cport-id in wValue field instead of
wIndex.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Tested-by: Fabien Parent <fparent@baylibre.com>
Reviewed-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>