drm: rcar-du: Print the error value when DRM/KMS init fails

This helps debugging probe failures.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
diff --git a/drivers/gpu/drm/rcar-du/rcar_du_drv.c b/drivers/gpu/drm/rcar-du/rcar_du_drv.c
index da1216a..780ca11 100644
--- a/drivers/gpu/drm/rcar-du/rcar_du_drv.c
+++ b/drivers/gpu/drm/rcar-du/rcar_du_drv.c
@@ -190,7 +190,7 @@
 	/* DRM/KMS objects */
 	ret = rcar_du_modeset_init(rcdu);
 	if (ret < 0) {
-		dev_err(&pdev->dev, "failed to initialize DRM/KMS\n");
+		dev_err(&pdev->dev, "failed to initialize DRM/KMS (%d)\n", ret);
 		goto done;
 	}