doc: Remove tab from SGML file

doc/src/sgml/func.sgml

@@ -15814,7 +15814,7 @@ postgres=# SELECT * FROM pg_xlogfile_name_offset(pg_stop_backup());
    <para>
     <function>pg_filenode_relation</> is the reverse of
     <function>pg_relation_filenode</>. Given a <quote>tablespace</> OID and
-	a <quote>filenode</>, it returns the associated relation's OID. For a table
+    a <quote>filenode</>, it returns the associated relation's OID. For a table
     in the database's default tablespace, the tablespace can be specified as 0.
    </para>