drm: Use plane->state->fb over plane->fb

Stop looking at plane->fb on atomic drivers. Use plane->state->fb
instead.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180322152313.6561-9-ville.syrjala@linux.intel.com
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
index fe09d62..ee03c1e 100644
--- a/drivers/gpu/drm/drm_atomic_helper.c
+++ b/drivers/gpu/drm/drm_atomic_helper.c
@@ -2670,7 +2670,7 @@ int drm_atomic_helper_disable_plane(struct drm_plane *plane,
 		goto fail;
 	}
 
-	if (plane_state->crtc && (plane == plane->crtc->cursor))
+	if (plane_state->crtc && plane_state->crtc->cursor == plane)
 		plane_state->state->legacy_cursor_update = true;
 
 	ret = __drm_atomic_helper_disable_plane(plane, plane_state);