docs: Fix "typo" introduced in 3f811c2d.

Reported-By: Michael Paquier
Discussion: CAB7nPqSco+RFw9C-VgbCpyurQB3OocS-fuTOa_gFnUy1EE-pyQ@mail.gmail.com

doc/src/sgml/catalogs.sgml

@@ -5579,7 +5579,7 @@
      </row>
 
      <row>
-      <entry><structfield>confirmed_flush</structfield></entry>
+      <entry><structfield>confirmed_flush_lsn</structfield></entry>
       <entry><type>pg_lsn</type></entry>
       <entry></entry>
       <entry>The address (<literal>LSN</literal>) up to which the logical