routeros: fix a small build error pointed out by clang

routeros: fix a small build error pointed out by clang

routeros.c:334:35: error: 'memset' call operates on objects of type 'cr_data_t' (aka 'struct cr_data_s') while the size is based on a different type 'cr_data_t *' (aka 'struct cr_data_s *') [-Werror,-Wsizeof-pointer-memaccess]
  memset (router_data, 0, sizeof (router_data));
          ~~~~~~~~~~~             ^~~~~~~~~~~
routeros.c:334:35: note: did you mean to dereference the argument to 'sizeof' (and multiply it by the number of elements)?
  memset (router_data, 0, sizeof (router_data));
                                  ^~~~~~~~~~~