anv: Fix typo in DestinationAlphaBlendFactor value
What does this MR do and why?
Workaround states that if Destination Alpha Blend
Factor==BLENDFACTOR_ZERO, instead use BLENDFACTOR_CONST_ALPHA with the
constant alpha set to 0.
We had typo while setting the DestinationAlphaBlendFactor, use
BLENDFACTOR_CONST_ALPHA instead of BLENDFACTOR_CONST_COLOR.