memoryPool::reserve<void>() always returns zero-sized object

[stgeke]

Suggested fix:

namespace occa {
  template <class T>
  occa::memory memoryPool::reserve(const dim_t entries) {
    if (std::is_void<T>::value) return reserve(entries, occa::dtype::byte); 
    return reserve(entries, occa::dtype::get<T>());
  }
}