fixed compile error

char *get_prefix_buf(int len, int node_id)

{

  char tmp_buf[sizeof("ndb_pid#########")+1];

  char *buf;

  if (node_id > 0)

    snprintf(tmp_buf, sizeof(tmp_buf), "ndb_%u", node_id);

  else

    snprintf(tmp_buf, sizeof(tmp_buf), "ndb_pid%u", getpid());

  tmp_buf[sizeof(tmp_buf)-1]= 0;

  char *buf= NdbConfig_AllocHomePath(len+strlen(tmp_buf));

  buf= NdbConfig_AllocHomePath(len+strlen(tmp_buf));

  strcat(buf, tmp_buf);

  return buf;

}