drm: drop unused drm_display_mode.private

drm_display_mode.private was only referenced in one place where
is was copied but never assigned.

Drop the copy and drop the field in drm_display_mode.
Adjust the comment of private_flags as is referred to the comment for
private.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Sean Paul <seanpaul@chromium.org>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200215183503.GA17310@ravnborg.org

drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c

@@ -516,7 +516,6 @@ static void _dpu_encoder_adjust_mode(struct drm_connector *connector,
 		if (cur_mode->vdisplay == adj_mode->vdisplay &&
 		    cur_mode->hdisplay == adj_mode->hdisplay &&
 		    drm_mode_vrefresh(cur_mode) == drm_mode_vrefresh(adj_mode)) {
-			adj_mode->private = cur_mode->private;
 			adj_mode->private_flags |= cur_mode->private_flags;
 		}
 	}

include/drm/drm_modes.h

@@ -371,20 +371,13 @@ struct drm_display_mode {
 	int crtc_vtotal;
 
 	/**
-	 * @private:
+	 * @private_flags:
 	 *
-	 * Pointer for driver private data. This can only be used for mode
+	 * Driver private flags. private_flags can only be used for mode
 	 * objects passed to drivers in modeset operations. It shouldn't be used
 	 * by atomic drivers since they can store any additional data by
 	 * subclassing state structures.
 	 */
-	int *private;
-
-	/**
-	 * @private_flags:
-	 *
-	 * Similar to @private, but just an integer.
-	 */
 	int private_flags;
 
 	/**