drm: rcar-du: fix backport bug

BugLink: http://bugs.launchpad.net/bugs/1711526

In the backport of commit 4f7b0d26 ("drm: rcar-du: Simplify and fix
probe error handling"), which is commit 8255d263 in this tree, the
error handling path was incorrect.  This patch fixes it up.
Reported-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Cc: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Cc: thongsyho <thong.ho.px@rvc.renesas.com>
Cc: Nhan Nguyen <nhan.nguyen.yb@renesas.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>

drivers/gpu/drm/rcar-du/rcar_du_drv.c

@@ -296,7 +296,7 @@ static int rcar_du_probe(struct platform_device *pdev)
 	mem = platform_get_resource(pdev, IORESOURCE_MEM, 0);
 	rcdu->mmio = devm_ioremap_resource(&pdev->dev, mem);
 	if (IS_ERR(rcdu->mmio))
-		ret = PTR_ERR(rcdu->mmio);
+		return PTR_ERR(rcdu->mmio);
 
 	/* DRM/KMS objects */
 	ddev = drm_dev_alloc(&rcar_du_driver, &pdev->dev);