backlight_device_register has been expecting a const "ops" argument, and using
it as such, since 9905a43b. Let's make the
remaining backlight_ops instances const.

Inspired by hunks of the grsecurity patch, updated for newer kernels.
Signed-off-by: NLionel Debroux <lionel_debroux@yahoo.fr>
Acked-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>