classmate-laptop: Fix extra keys hardware id.

Since ACPI devices ids were changed to use always upper-case letters, the ACPI
id of the extra keys (FNBT0000) was not maching the one defined in the driver
(FnBT0000), causing the extra keys not to work.

The patch replaces the driver id with the one reported by ACPI, fixing the
problem.

Signed-off-by: Miguel Gómez <magomez@igalia.com>
Signed-off-by: Matthew Garrett <mjg@redhat.com>