restore correct sound_prefix in default config broken in svn r16241

git-svn-id: http://svn.freeswitch.org/svn/freeswitch/trunk@16609 d0543943-73ff-0310-b7d9-9358b9ac24b2

conf/vars.xml

@@ -15,6 +15,8 @@
   <X-PRE-PROCESS cmd="set" data="default_password=1234"/>
   <!-- Did you change it yet? -->
 
+  <X-PRE-PROCESS cmd="set" data="sound_prefix=$${sounds_dir}/en/us/callie"/>
+
   <!--
       This setting is what sets the default domain FreeSWITCH will use if all else fails.