backlight: constify backlight_ops

backlight_device_register has been expecting a const "ops" argument, and using
it as such, since 9905a43b2d563e6f89e4c63c4278ada03f2ebb14. Let's make the
remaining backlight_ops instances const.

Inspired by hunks of the grsecurity patch, updated for newer kernels.

Signed-off-by: Lionel Debroux <lionel_debroux@yahoo.fr>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
diff --git a/drivers/acpi/video.c b/drivers/acpi/video.c
index 5cd0228..15a0fde 100644
--- a/drivers/acpi/video.c
+++ b/drivers/acpi/video.c
@@ -260,7 +260,7 @@
 				vd->brightness->levels[request_level]);
 }
 
-static struct backlight_ops acpi_backlight_ops = {
+static const struct backlight_ops acpi_backlight_ops = {
 	.get_brightness = acpi_video_get_brightness,
 	.update_status  = acpi_video_set_brightness,
 };