drm: renesas: shmobile: Improve error handling

Prepare for DT conversion, where panel probe can be deferred, by
streamlining error propagation and handling:
  - Use dev_err_probe() to avoid printing error messages in case of
    probe deferral,
  - Propagate errors where needed.
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/6dfac76e5b1c7dda3f96801ce83845a4235e2ccd.1694767209.git.geert+renesas@glider.be

drivers/gpu/drm/renesas/shmobile/shmob_drm_drv.c

@@ -253,7 +253,8 @@ static int shmob_drm_probe(struct platform_device *pdev)
 
 	ret = shmob_drm_modeset_init(sdev);
 	if (ret < 0) {
-		dev_err(&pdev->dev, "failed to initialize mode setting\n");
+		dev_err_probe(&pdev->dev, ret,
+			      "failed to initialize mode setting\n");
 		goto err_free_drm_dev;
 	}
 

drivers/gpu/drm/renesas/shmobile/shmob_drm_kms.c

@@ -157,9 +157,17 @@ int shmob_drm_modeset_init(struct shmob_drm_device *sdev)
 	if (ret)
 		return ret;
 
-	shmob_drm_crtc_create(sdev);
-	shmob_drm_encoder_create(sdev);
-	shmob_drm_connector_create(sdev, &sdev->encoder);
+	ret = shmob_drm_crtc_create(sdev);
+	if (ret < 0)
+		return ret;
+
+	ret = shmob_drm_encoder_create(sdev);
+	if (ret < 0)
+		return ret;
+
+	ret = shmob_drm_connector_create(sdev, &sdev->encoder);
+	if (ret < 0)
+		return ret;
 
 	drm_kms_helper_poll_init(sdev->ddev);