pwm: cros-ec: Drop documentation for dropped struct member

Recently an unused member was removed from struct cros_ec_pwm_device,
but the kernel doc wasn't adapted accordingly. Catch up and drop the
documentation, too.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202312190757.O4M9dsln-lkp@intel.com/


Fixes: 6c4406ce ("pwm: cros-ec: Drop unused member from driver private data")
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: Tzung-Bi Shih <tzungbi@kernel.org>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>