pwm: cros-ec: Drop unused member from driver private data

.dev is unused since the driver was introduced in commit 1f0d3bb0
("pwm: Add ChromeOS EC PWM driver"). Drop it.

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>