modules/db_postgres: Fixed copy-and-paste error in module documentation

(cherry picked from commit c5a51e4236498cfe3ca31c8aae96d3b422a9da23)

modules/db_postgres/README

@@ -85,7 +85,7 @@ Chapter 1. Admin Guide
 
    Example 1.1. Set retries parameter
 ...
-modparam("db_mysql", "retries", 3)
+modparam("db_postgres", "retries", 3)
 ...
 
 4. Functions

modules/db_postgres/doc/db_postgres_admin.xml

@@ -76,7 +76,7 @@
 		<title>Set <varname>retries</varname> parameter</title>
 		<programlisting format="linespecific">
 ...
-modparam("db_mysql", "retries", 3)
+modparam("db_postgres", "retries", 3)
 ...
 </programlisting>
 		</example>