drm/qxl: add drm_gem_plane_helper_prepare_fb

We could need to wait for the pin to complete here.

Signed-off-by: Christian König <[e-mail]>
Cc: Dave Airlie <[e-mail]>
Cc: Gerd Hoffmann <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Reviewed-by: Daniel Vetter <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/qxl/qxl_display.c

···
 #include <drm/drm_plane_helper.h>
 #include <drm/drm_probe_helper.h>
 #include <drm/drm_simple_kms_helper.h>
+#include <drm/drm_gem_atomic_helper.h>
 
 #include "qxl_drv.h"
 #include "qxl_object.h"
···
 	struct qxl_device *qdev = to_qxl(plane->dev);
 	struct drm_gem_object *obj;
 	struct qxl_bo *user_bo;
+	int ret;
 
 	if (!new_state->fb)
 		return 0;
···
 		qxl_free_cursor(old_cursor_bo);
 	}
 
-	return qxl_bo_pin(user_bo);
+	ret = qxl_bo_pin(user_bo);
+	if (ret)
+		return ret;
+
+	return drm_gem_plane_helper_prepare_fb(plane, new_state);
 }
 
 static void qxl_plane_cleanup_fb(struct drm_plane *plane,