msi-laptop: Disable brightness control for new EC

It seems that existing brightness control works only for old EC models.
On newer ones auto_brightness access always timeouts and lcd_level
always shows 0. So disable brightness control for new EC models. It
works fine with ACPI video driver anyway.

Signed-off-by: Maxim Mikityanskiy <maxtram95@gmail.com>
Signed-off-by: Lee, Chun-Yi <jlee@suse.com>
Signed-off-by: Matthew Garrett <matthew.garrett@nebula.com>