[gentoo-dev] One more USE flag added to desktop make.defau..

Since USE dvd was there already, I previously dropped in the a52 codec
required for standard DVD support. Forgot to add one USE flag, beandog
nicely added it today. It's: USE dts

That's also a default DVD codec, it pulls in basically one library
small, media-libs/libdca for sounds.

Thanks, Samuli