We should stop our worker thread while we're suspended.  If we don't
then we'll get messages like:

  cros-ec-spi spi5.0: spi transfer failed: -108
  cros-ec-spi spi5.0: cs-deassert spi transfer failed: -108
  cros-ec-ctl cros-ec-ctl.0.auto: EC communication failed
Signed-off-by: Douglas Anderson <dianders@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>