msvfw32: Cast-qual warning fix

[Andrew Talbot]

Dmitry Timoshkov wrote:

> "Andrew Talbot" <Andrew.Talbot at talbotville.com> wrote:
> 
>> The last formal argument of MCIWndCreate() is not const-qualified in the
>> SDK.
> 
> It is in my version of the PSDK headers, but it is not in the PSDK docs.
> 

Not having access to any version of the SDK, my only source of reference is
the MSDN web site.

-- Andy.