mfd: cros_ec: Remove parent field

Parent and device were pointing to the same device structure.

Parent is unused, removed.

Signed-off-by: Gwendal Grignou <gwendal@chromium.org>
Tested-by: Stephen Barber <smbarber@chromium.org>
Tested-by: Heiko Stuebner <heiko@sntech.de>
Tested-by: Gwendal Grignou <gwendal@chromium.org>
Reviewed-by: Puthikorn Voravootivat <puthik@chromium.org>
Signed-off-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Signed-off-by: Lee Jones <lee.jones@linaro.org>