bslalg_hashtableimputil.t: Fix -Wformat warning.

Fixes the following:

```
../groups/bsl/bslalg/bslalg_hashtableimputil.t.cpp: In function ‘void debugPrint(const BloombergLP::bslalg::HashTableAnchor&)’:
../groups/bsl/bslalg/bslalg_hashtableimputil.t.cpp:275: warning: format ‘%d’ expects type ‘int’, but argument 2 has type ‘size_t’ [-Wformat]
../groups/bsl/bslalg/bslalg_hashtableimputil.t.cpp:275: warning: format ‘%d’ expects type ‘int’, but argument 2 has type ‘size_t’ [-Wformat]
```