fbdev/radeonfb: Use hardware device as backlight parent

Use the hardware device in struct fb_info.device as parent of the
backlight device. Aligns the driver with the rest of the codebase
and prepares fbdev for making struct fb_info.dev optional.

v2:
	* add Cc: tag (Dan)
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230613110953.24176-23-tzimmermann@suse.de

drivers/video/fbdev/aty/radeon_backlight.c

@@ -147,7 +147,7 @@ void radeonfb_bl_init(struct radeonfb_info *rinfo)
 	memset(&props, 0, sizeof(struct backlight_properties));
 	props.type = BACKLIGHT_RAW;
 	props.max_brightness = FB_BACKLIGHT_LEVELS - 1;
-	bd = backlight_device_register(name, rinfo->info->dev, pdata,
+	bd = backlight_device_register(name, rinfo->info->device, pdata,
 				       &radeon_bl_data, &props);
 	if (IS_ERR(bd)) {
 		rinfo->info->bl_dev = NULL;