Platform: fix samsung-laptop DMI identification for N220 model

This is a follow-up for commit 78a7539b, which didn't cover the
Samsung N220 laptop. With this backlight brightness works nicely
on the N220 netbook.

Signed-off-by: Raul Gutierrez Segales <rgs@collabora.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Matthew Garrett <mjg@redhat.com>