ovs-vsctl: Prevent uninitialized variable warning.

The compiler warns about next_cfg being uninitialized but in the cases
where it is unset we will never reach the point where it is used.  This
just sets next_cfg to 0 to stop the whining.

utilities/ovs-vsctl.c

@@ -1488,7 +1488,7 @@ do_vsctl(int argc, char *argv[], struct ovsdb_idl *idl)
     const struct ovsrec_open_vswitch *ovs;
     enum ovsdb_idl_txn_status status;
     struct ds comment, *output;
-    int64_t next_cfg;
+    int64_t next_cfg = 0;
     int n_output;
     int i, start;