gpu: ipu-v3: default to id 0 on missing OF alias

This is better than storing -ENODEV in the id number. This fixes SoCs
with only one IPU that don't specify an IPU alias in the device tree.
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>

drivers/gpu/ipu-v3/ipu-common.c

@@ -1401,6 +1401,8 @@ static int ipu_probe(struct platform_device *pdev)
 		return -ENODEV;
 
 	ipu->id = of_alias_get_id(np, "ipu");
+	if (ipu->id < 0)
+		ipu->id = 0;
 
 	if (of_device_is_compatible(np, "fsl,imx6qp-ipu") &&
 	    IS_ENABLED(CONFIG_DRM)) {