mfd: cros_ec: Update module description

mfd: cros_ec: Update module description

The module description can be backtracked to commit e7c256fbfb15
("platform/chrome: Add Chrome OS EC userspace device interface").

The description became out-of-date after a bunch of changes e.g:

- commit 5668bfdd90cd ("platform/chrome: cros_ec_dev - Register cros-ec sensors").
- commit ea01a31b9058 ("cros_ec: Split cros_ec_devs module").
- commit 5e0115581bbc ("cros_ec: Move cros_ec_dev module to drivers/mfd").

Update the description.

Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>
Link: https://lore.kernel.org/r/20240822121539.4265-1-tzungbi@kernel.org
Signed-off-by: Lee Jones <lee@kernel.org>