Bug 1021265. Fix DisplayLink version expansion code. r=Bas,a=lawrence

GFX_DRIVER_VERSION(8,6,..) expands to 8.0006....
but ParseVersion(8.6,...) gives 8.5000...
This was an unfortunate error. Having better static typing
of versions would have helped here.

--HG--
extra : amend_source : 5082be5161cbb2c02301f5647a578be484afe860