permissions: Fix typo in documentation

modules/permissions/README

@@ -339,7 +339,7 @@ Chapter 1. Admin Guide
    peer_tag_avp module parameter has been defined.
 
    Rules are stored in a database table specified by module parameters.
-   There also exists a module parameter dm_mode that determines if rules
+   There also exists a module parameter db_mode that determines if rules
    are cached into memory for faster matching or if database is consulted
    for each invocation of allow_trusted function call.
 

modules/permissions/doc/permissions_admin.xml

@@ -247,7 +247,7 @@
 		<para>
 		Rules are stored in a database table specified by module
 		parameters.  There also exists a module parameter
-	        <varname>dm_mode</varname> that
+	        <varname>db_mode</varname> that
 		determines if rules are cached into memory for faster
 		matching or if database is consulted for each invocation
 		of allow_trusted function call.