mesa/st: Don't use 4bits for GL_UNSIGNED_BYTE_3_3_2(_REV)

4bits and 3bits quantitization values differ significantly for
values other than 0 and 1.

Fixes piglit draw-pixels for softpipe/llvmpipe.

NOTE: Probably a candidate for stable branches.

Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Marek Olšák <maraeo@gmail.com>
1 file changed