drm/radeon: constify more struct drm_*_helper funcs pointers

Some non-const pointers were added since the last constification, fix
them.
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/radeon/radeon_connectors.c

@@ -751,7 +751,7 @@ static int radeon_connector_set_property(struct drm_connector *connector, struct
 		if (connector->encoder)
 			radeon_encoder = to_radeon_encoder(connector->encoder);
 		else {
-			struct drm_connector_helper_funcs *connector_funcs = connector->helper_private;
+			const struct drm_connector_helper_funcs *connector_funcs = connector->helper_private;
 			radeon_encoder = to_radeon_encoder(connector_funcs->best_encoder(connector));
 		}
 
@@ -762,7 +762,7 @@ static int radeon_connector_set_property(struct drm_connector *connector, struct
 
 		if (connector->encoder->crtc) {
 			struct drm_crtc *crtc  = connector->encoder->crtc;
-			struct drm_crtc_helper_funcs *crtc_funcs = crtc->helper_private;
+			const struct drm_crtc_helper_funcs *crtc_funcs = crtc->helper_private;
 			struct radeon_crtc *radeon_crtc = to_radeon_crtc(crtc);
 
 			radeon_crtc->output_csc = radeon_encoder->output_csc;

drivers/gpu/drm/radeon/radeon_dp_mst.c

@@ -604,7 +604,7 @@ radeon_dp_create_fake_mst_encoder(struct radeon_connector *connector)
 	struct radeon_encoder *radeon_encoder;
 	struct radeon_encoder_mst *mst_enc;
 	struct drm_encoder *encoder;
-	struct drm_connector_helper_funcs *connector_funcs = connector->base.helper_private;
+	const struct drm_connector_helper_funcs *connector_funcs = connector->base.helper_private;
 	struct drm_encoder *enc_master = connector_funcs->best_encoder(&connector->base);
 
 	DRM_DEBUG_KMS("enc master is %p\n", enc_master);