Apply suggestions from code review

Co-authored-by: Gina Peter Banyard <girgias@php.net>

Author: ndossche

reference/xmlreader/xmlreader/fromstream.xml

@@ -43,7 +43,7 @@
     <term><parameter>flags</parameter></term>
     <listitem>
      <simpara>
-      A bitmask of the <link linkend="libxml.constants">LIBXML_*</link>
+      A bitmask of the <constant>LIBXML_<replaceable>*</replaceable></constant>
       constants.
      </simpara>
     </listitem>

reference/xmlwriter/xmlwriter/tomemory.xml

@@ -15,6 +15,7 @@
    Creates a new <classname>XMLWriter</classname> using memory for string output.
   </simpara>
  </refsect1>
+
  <refsect1 role="parameters">
   &reftitle.parameters;
   &no.function.parameters;