mmdevapi/tests: Fix wrong buffer unit and memory leaks.

Hi,
> - nBlockAlign is wrong since data is counted in frames, not bytes.

I forgot to comment that I introduced the 10x multiplicator to
convince myself that GetData accepts buffer sizes larger than the
default 10ms chunk returned by GetDevicePeriod.  That is reasonable, but
not guaranteed when I read MSDN (the API would work with small buffers too).

Regards,
    Jörg Höhle