Fixes broken link in updating docs

Author: opayne1

updating/understanding-openshift-updates.adoc

@@ -18,5 +18,7 @@ include::modules/update-common-terms.adoc[leveloffset=+1]
 .Additional resources
 
 * xref:../post_installation_configuration/machine-configuration-tasks.adoc#machine-config-overview-post-install-machine-configuration-tasks[Machine config overview]
+ifdef::openshift-enterprise[]
 * xref:../updating/updating-restricted-network-cluster.adoc#update-service-overview_updating-restricted-network-cluster[About the OpenShift Update Service]
+endif::openshift-enterprise[]
 * xref:../updating/understanding-upgrade-channels-release.adoc#understanding-upgrade-channels_understanding-upgrade-channels-releases[Update channels and releases]