drm/i915: Don't cast away const

The connector state passed to .atomic_get_property() is const.
We should preserve that when downcasting to our version.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240307151810.24208-3-ville.syrjala@linux.intel.comReviewed-by: Jani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/i915/display/intel_atomic.c

@@ -62,7 +62,7 @@ int intel_digital_connector_atomic_get_property(struct drm_connector *connector,
 {
 	struct drm_device *dev = connector->dev;
 	struct drm_i915_private *dev_priv = to_i915(dev);
-	struct intel_digital_connector_state *intel_conn_state =
+	const struct intel_digital_connector_state *intel_conn_state =
 		to_intel_digital_connector_state(state);
 
 	if (property == dev_priv->display.properties.force_audio)