drm/vc4: Fix NULL deref in HDMI init error path

If you make it here other than through err_destroy_encoder, vc4->hdmi
is still NULL.

Signed-off-by: Eric Anholt <eric@anholt.net>

drivers/gpu/drm/vc4/vc4_hdmi.c

@@ -573,7 +573,7 @@ err_unprepare_hsm:
 err_unprepare_pix:
 	clk_disable_unprepare(hdmi->pixel_clock);
 err_put_i2c:
-	put_device(&vc4->hdmi->ddc->dev);
+	put_device(&hdmi->ddc->dev);
 
 	return ret;
 }