wined3d: Fix ATI dx10 cards max varying quirk

[Robert Key]

I fiddled around with the test and I was able to use varying vec4 
var_in[13] as a max in one array. 14 - 16 resulted in a segmentation 
fault and 17 resulted in glLinK failure error.

I was able to create a second array of varying vec4 testa[3] though 
and it compiled successfully resulting in 64 varyings. I'll attach what I 
did.