llvmpipe/fs: fix regression in sample mask handling from tgsi removal.
What does this MR do and why?
llvmpipe/fs: fix regression in sample mask handling from tgsi removal.
This got the bits the wrong way, dEQP-VK.rasterization.frag_side_effects.color_at_beginning.sample_mask_after
Fixes: a63c2daf ("llvmpipe/fs: start using nir info in some places.")