backlight: constify backlight_ops

backlight_device_register has been expecting a const "ops" argument, and using
it as such, since 9905a43b2d. 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>

drivers/video/backlight/max8925_bl.c

@@ -92,7 +92,7 @@ static int max8925_backlight_get_brightness(struct backlight_device *bl)
 	return ret;
 }
 
-static struct backlight_ops max8925_backlight_ops = {
+static const struct backlight_ops max8925_backlight_ops = {
 	.options	= BL_CORE_SUSPENDRESUME,
 	.update_status	= max8925_backlight_update_status,
 	.get_brightness	= max8925_backlight_get_brightness,