nir/lower_bit_size: Don't cast comparison results

Some ALU ops (comparisons being the primary example) have a fixed
bit-size destination and, in that case, we don't want to insert a
conversion on the destination.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7482>
1 file changed