Fix hardcoded constant in skip_stride computation.
Fix hardcoded constant in skip_stride computation.

xiphmont/daala,kodabb/daala,ycho/daala,HeadhunterXamd/daala,jmvalin/daala,xiph/daala,luctrudeau/daala,xiph/daala,HeadhunterXamd/daala,jmvalin/daala,luctrudeau/daala,HeadhunterXamd/daala,xiph/daala,kodabb/daala,jmvalin/daala,ycho/daala,ycho/daala,KyleSiefring/daala,HeadhunterXamd/daala,ycho/daala,kodabb/daala,kodabb/daala,xiph/daala,KyleSiefring/daala,KyleSiefring/daala,jmvalin/daala,xiphmont/daala,KyleSiefring/daala,HeadhunterXamd/daala,luctrudeau/daala,xiphmont/daala,KyleSiefring/daala,luctrudeau/daala,kodabb/daala,luctrudeau/daala,xiphmont/daala,xiph/daala,jmvalin/daala,ycho/daala,xiphmont/daala