drm/radeon: Fix KMS legacy backlight support if CONFIG_BACKLIGHT_CLASS_DEVICE=m.

Signed-off-by: Michel Dänzer <daenzer@vmware.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/radeon/radeon_legacy_encoders.c

@@ -269,7 +269,7 @@ static const struct drm_encoder_helper_funcs radeon_legacy_lvds_helper_funcs = {
 	.disable = radeon_legacy_encoder_disable,
 };
 
-#ifdef CONFIG_BACKLIGHT_CLASS_DEVICE
+#if defined(CONFIG_BACKLIGHT_CLASS_DEVICE) || defined(CONFIG_BACKLIGHT_CLASS_DEVICE_MODULE)
 
 #define MAX_RADEON_LEVEL 0xFF