Fix reference to r2db_hash_map

db-config.php

@@ -15,4 +15,4 @@ include_once('r2db/db-backends.php');
 noblogs_load_global_dataset();
 
 // Add all the sharded blog databases.
-$wpdb_reverse_backend_map = noblogs_load_backends($wpdb->hash_map);
+$wpdb_reverse_backend_map = noblogs_load_backends($r2db_hash_map);