Reboot or shutdown during delayed works could corrupt communication with
EC and certain I2C controller may not be able to recover from the error
state.

This patch registers a shutdown callback used to cancel the debugfs log
worker thread.
Signed-off-by: Daniel Hung-yu Wu <hywu@chromium.org>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>