drm: make crtc/encoder/connector/plane helper_private a const pointer

They're only used to store const pointers anyway. This helps to keep
Ville and the compiler happy.

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>
diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
index 7b5c661..97c33b4 100644
--- a/include/drm/drm_crtc.h
+++ b/include/drm/drm_crtc.h
@@ -467,7 +467,7 @@
 	int framedur_ns, linedur_ns, pixeldur_ns;
 
 	/* if you are using the helper */
-	void *helper_private;
+	const void *helper_private;
 
 	struct drm_object_properties properties;
 
@@ -597,7 +597,7 @@
 	struct drm_crtc *crtc;
 	struct drm_bridge *bridge;
 	const struct drm_encoder_funcs *funcs;
-	void *helper_private;
+	const void *helper_private;
 };
 
 /* should we poll this connector for connects and disconnects */
@@ -701,7 +701,7 @@
 	/* requested DPMS state */
 	int dpms;
 
-	void *helper_private;
+	const void *helper_private;
 
 	/* forced on connector */
 	struct drm_cmdline_mode cmdline_mode;
@@ -864,7 +864,7 @@
 
 	enum drm_plane_type type;
 
-	void *helper_private;
+	const void *helper_private;
 
 	struct drm_plane_state *state;
 };