nir/algebraic: Partially revert 3f782cdd2591

I'm not sure what the logic was, but there is no opportunity for
anything to flush to zero here.  'a' is a Boolean value, and b2f
produces 1.0 or 0.0.

This was originally part of
https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/3765/.

Reviewed-by: Matt Turner <mattst88@gmail.com>
Cc: Andres Gomez <agomez@igalia.com>
Cc: Samuel Iglesias Gonsálvez <siglesias@igalia.com>
Cc: Connor Abbott <cwabbott0@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8910>
1 file changed