drm/atmel-hlcdc: always iterate over the first 4 output endpoints

This enables more flexible devicetrees. You can e.g. have two output
nodes where one is not enabled, without the ordering affecting things.

Prior to this patch the active nodes had to have endpoint id zero and
upwards consecutively.

Signed-off-by: Peter Rosin <peda@axentia.se>
Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180825085620.10566-4-peda@axentia.se

drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_output.c

@@ -78,12 +78,23 @@ static int atmel_hlcdc_attach_endpoint(struct drm_device *dev, int endpoint)
 int atmel_hlcdc_create_outputs(struct drm_device *dev)
 {
 	int endpoint, ret = 0;
+	int attached = 0;
 
-	for (endpoint = 0; !ret; endpoint++)
+	/*
+	 * Always scan the first few endpoints even if we get -ENODEV,
+	 * but keep going after that as long as we keep getting hits.
+	 */
+	for (endpoint = 0; !ret || endpoint < 4; endpoint++) {
 		ret = atmel_hlcdc_attach_endpoint(dev, endpoint);
+		if (ret == -ENODEV)
+			continue;
+		if (ret)
+			break;
+		attached++;
+	}
 
 	/* At least one device was successfully attached.*/
-	if (ret == -ENODEV && endpoint)
+	if (ret == -ENODEV && attached)
 		return 0;
 
 	return ret;