freedreno/a6xx: Fix non-mipmap filtering selection.
We were clamping the LOD to force non-mipmap filtering, but that means that the HW doesn't get to select between the min and mag filters. Setting MIPFILTER_LINEAR_FAR appears to force non-mipmap filtering.
Fixes all failures in dEQP-GLES2.functional.texture.filtering.2d.*