drm/core: Set legacy_cursor_update in drm_atomic_helper_disable_plane.

legacy_cursor_update was being set in restore_fbdev_mode_atomic which was
probably unintended. Fix this by only setting it in the function that needs it.

This oversight was introduced in

commit bbb1e524
Author: Rob Clark <robdclark@gmail.com>
Date:   Tue Aug 25 15:35:58 2015 -0400

    drm/fb-helper: atomic restore_fbdev_mode()...
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
[Jani: checkpatch fix]
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1447237751-9663-2-git-send-email-maarten.lankhorst@ubuntu.com

drivers/gpu/drm/drm_atomic_helper.c

@@ -1553,6 +1553,9 @@ int drm_atomic_helper_disable_plane(struct drm_plane *plane)
 		goto fail;
 	}
 
+	if (plane_state->crtc && (plane == plane->crtc->cursor))
+		plane_state->state->legacy_cursor_update = true;
+
 	ret = __drm_atomic_helper_disable_plane(plane, plane_state);
 	if (ret != 0)
 		goto fail;
@@ -1605,9 +1608,6 @@ int __drm_atomic_helper_disable_plane(struct drm_plane *plane,
 	plane_state->src_h = 0;
 	plane_state->src_w = 0;
 
-	if (plane->crtc && (plane == plane->crtc->cursor))
-		plane_state->state->legacy_cursor_update = true;
-
 	return 0;
 }