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

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--
branch : GECKO331_2014103013_RELBRANCH