V4L: fix return value of register video func

From: Henrik Kretzschmar <[email protected]>

If a wrong device type is used with video_register_device_index() it should better return an error number, instead of a constant.

index 6f36006..0320fb8 100644
@@ -281,7 +281,7 @@ int video_register_device_index(struct video_device *vfd, int type, int nr,

	default:
		printk(KERN_ERR "%s called with unknown type: %d\n",
		       __func__, type);
-		return -1;
+		return -EINVAL;
	}

	/* pick a minor number */