msacm: pcm compatibility patch

[Mike Hearn]

On Sat, 11 Dec 2004 09:29:21 -0500, Robert Reif wrote:
> The Microsoft code will not read and/or
> write the entire contents of the buffers under some
> circumstances.  Duplicating this behavior lead to the code I
> have presented.

What bugs did this behaviour cause? If it's purely a matter of correctness
with no known negative side-effects I'm not sure it should go in ...