mfd: cros_ec_dev: Add missing mfd_remove_devices() call in remove

[ Upstream commit 18e294dd ]

The driver adds different MFD child devices via mfd_add_devices() and
hence it is required to call mfd_remove_devices() to remove MFD child
devices.

Fixes: 5e011558 ("cros_ec: Move cros_ec_dev module to drivers/mfd")
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>