mmdevapi/tests: Use RegQueryValueExW() for compatibility with Windows XP.

[Andrew Eikum]

On Wed, Apr 20, 2016 at 10:17:49PM +0200, Francois Gouget wrote:
> On Wed, 20 Apr 2016, Andrew Eikum wrote:
> 
> > mmdevapi doesn't exist on winxp. I'm not opposed to this change, but
> > does it matter?
> 
> It fixes this failure:
> https://testbot.winehq.org/JobDetails.pl?Key=22355
> 
> Arguably the TestBot should have realized that mmdevapi is missing and 
> skipped running the test altogether. But in the meantime this means 
> further mmdevapi patches will not return spurious failures.
> 

Works for me.

Signed-off-by: Andrew Eikum <aeikum at codeweavers.com>