drm/vc4: hdmi: Don't access the connector state in reset if kmalloc fails

drm_atomic_helper_connector_reset uses kmalloc which, from an API
standpoint, can fail, and thus setting connector->state to NULL.
However, our reset hook then calls drm_atomic_helper_connector_tv_reset
that will access connector->state without checking if it's a valid
pointer or not.

Make sure we don't end up accessing a NULL pointer.
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Suggested-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20201215154243.540115-5-maxime@cerno.tech

drivers/gpu/drm/vc4/vc4_hdmi.c

@@ -171,7 +171,9 @@ static int vc4_hdmi_connector_get_modes(struct drm_connector *connector)
 static void vc4_hdmi_connector_reset(struct drm_connector *connector)
 {
 	drm_atomic_helper_connector_reset(connector);
-	drm_atomic_helper_connector_tv_reset(connector);
+
+	if (connector->state)
+		drm_atomic_helper_connector_tv_reset(connector);
 }
 
 static const struct drm_connector_funcs vc4_hdmi_connector_funcs = {