While Go has goto for tricky situations like this, because it has defer you don't have to use it often, assuming the free calls were needed (and the vars were not going to be GC'd):

    defer SSLFreeBuffer(&hashCtx)
    defer SSLFreeBuffer(&signedHashes)
    if err = SSLHashSHA1.update(&hashCtx, &serverRandom); err != nil {
      return err;
    } else if err = SSLHashSHA1.update(&hashCtx, &signedParams); err != nil {
      return err;
    } else if err = SSLHashSHA1.final(&hashCtx, &hashOut); err != nil {
      return err;
    }
    return nil;
  }