drm/tegra: Silence expected errors on IOMMU attach

Subdevices may not be hooked up to an IOMMU via device tree. Detect such
situations and avoid confusing users by not emitting an error message.

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Thierry Reding <treding@nvidia.com>

drivers/gpu/drm/tegra/dc.c

@@ -2017,7 +2017,7 @@ static int tegra_dc_init(struct host1x_client *client)
 		dev_warn(dc->dev, "failed to allocate syncpoint\n");
 
 	err = host1x_client_iommu_attach(client);
-	if (err < 0) {
+	if (err < 0 && err != -ENODEV) {
 		dev_err(client->dev, "failed to attach to domain: %d\n", err);
 		return err;
 	}