drm/armada: constify struct drm_encoder_helper_funcs pointer

Not to be modified.
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/armada/armada_output.h

@@ -9,7 +9,7 @@
 #define ARMADA_CONNETOR_H
 
 #define encoder_helper_funcs(encoder) \
-	((struct drm_encoder_helper_funcs *)encoder->helper_private)
+	((const struct drm_encoder_helper_funcs *)encoder->helper_private)
 
 struct armada_output_type {
 	int connector_type;