platform/chrome: cros_ec_typec: Flush pending work

When a PD notifier event arrives, a new work event won't be enqueued if
the current one hasn't completed. This could lead to dropped events.

So, flush any pending work before scheduling the new instance.

Signed-off-by: Prashant Malani <pmalani@chromium.org>
Link: https://lore.kernel.org/r/20210211193221.610867-1-pmalani@chromium.org


Signed-off-by: Benson Leung <bleung@chromium.org>