drm/kirin: Checking for IS_ERR() instead of NULL

The of_graph_get_remote_node() function doesn't return error pointers,
it returns NULL on error so I've updated the check.

Fixes: 86418f90 ("drm: convert drivers to use of_graph_get_remote_node")
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NSean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20171005125751.jvtjms62vbtxuvak@mwanda

drivers/gpu/drm/hisilicon/kirin/kirin_drm_drv.c

@@ -237,8 +237,8 @@ static int kirin_drm_platform_probe(struct platform_device *pdev)
 	}
 
 	remote = of_graph_get_remote_node(np, 0, 0);
-	if (IS_ERR(remote))
-		return PTR_ERR(remote);
+	if (!remote)
+		return -ENODEV;
 
 	drm_of_component_match_add(dev, &match, compare_of, remote);
 	of_node_put(remote);