drm/i915/hdcp: Add encoder check in hdcp2_get_capability

Add encoder check in intel_hdcp2_get_capability to avoid
null pointer error.
Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>
Reviewed-by: Dnyaneshwar Bhadane <dnyaneshwar.bhadane@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240722064451.3610512-3-suraj.kandpal@intel.com

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

@@ -675,8 +675,15 @@ static
 int intel_dp_hdcp2_get_capability(struct intel_connector *connector,
 				  bool *capable)
 {
-	struct intel_digital_port *dig_port = intel_attached_dig_port(connector);
-	struct drm_dp_aux *aux = &dig_port->dp.aux;
+	struct intel_digital_port *dig_port;
+	struct drm_dp_aux *aux;
+
+	*capable = false;
+	if (!intel_attached_encoder(connector))
+		return -EINVAL;
+
+	dig_port = intel_attached_dig_port(connector);
+	aux = &dig_port->dp.aux;
 
 	return _intel_dp_hdcp2_get_capability(aux, capable);
 }