pan/bi: Don't use funny round modes in tests

To prepare for defeaturing round modes, replace uses of round-to-positive with
round-to-even in our unit tests. This doesn't meaningfully impact test coverage;
there is no way to generate that round mode.

Signed-off-by: Alyssa Rosenzweig <alyssa@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/15187>
2 files changed