Ticket 623 - cleanAllRUV task fails to cleanup config upon completion

Bug description: coverity reported "13158 - Logically dead code'

Fix description: csn_as_string returns allocated csn string,
which needs to be reassigned to csnstr.

https://fedorahosted.org/389/ticket/623

Reviewed by Nathan (Thank you!!)

ldap/servers/plugins/replication/repl5_replica_config.c

@@ -2396,7 +2396,7 @@ delete_cleaned_rid_config(cleanruv_data *clean_data)
     /*
      *  If there is no maxcsn, set the proper csnstr
      */
-    csn_as_string(clean_data->maxcsn, PR_FALSE, csnstr);
+    csnstr = csn_as_string(clean_data->maxcsn, PR_FALSE, csnstr);
     if(csnstr == NULL || csn_get_replicaid(clean_data->maxcsn) == 0){
         csnstr = slapi_ch_strdup("00000000000000000000");
     }