buffer::set_final_data accepts weak_ptr<T>, not <T[]>

[fknorr]

See [4.7.2.1]:

The finalData points to where the outcome of all the buffer processing is going to be copied to at destruction time, if the buffer was involved with a write accessor.

Destination can be either an output iterator or a std::weak_ptr<T>.

Note that a raw pointer is a special case of output iterator and thus defines the host memory to which the result is to be copied.

Not sure if this was different in an earlier spec revision.