platform/chrome: wilco_ec: Fix unregistration order

The unregistration should happen in the opposite order of
the registration, so change it accordingly.

No real issue has been noticed, but it is good practice to
keep the correct unregistration order.

Signed-off-by: Daniel Campello <campello@chromium.org>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>