Fix id for TopologyDescription::TYPE_LOAD_BALANCED

Fixes a build failure from bd6e660

Author: jmikola

reference/mongodb/mongodb/driver/topologydescription.xml

@@ -121,7 +121,7 @@
      </listitem>
     </varlistentry>
 
-    <varlistentry xml:id="mongodb-driver-topologydescription.constants.type-load-balancer">
+    <varlistentry xml:id="mongodb-driver-topologydescription.constants.type-load-balanced">
      <term><constant>MongoDB\Driver\TopologyDescription::TYPE_LOAD_BALANCED</constant></term>
      <listitem>
       <para>Load balanced topology, returned by <methodname>MongoDB\Driver\TopologyDescription::getType</methodname>.</para>