platform/chrome: cros_ec_lpc_mec: Fix kernel-doc comment first line

kernel-doc comments have a prescribed format. To be _particularly_ correct
we should also capitalise the brief description and terminate it with a
period.

Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Reviewed-by: Nick Crews <ncrews@chromium.org>