i965/fs: Don't propagate conditional modifiers from integer compares to adds

No shader-db changes on any Intel platform... which probably explains
why no bugs have been bisected to this problem since it landed in Mesa
18.1. :( The commit mentioned below is in 18.2, so 18.1 would need a
slightly different fix (due to code refactoring).

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Fixes: 77f269bb "i965/fs: Refactor propagation of conditional modifiers from compares to adds"
Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com> (reviewed the original patch)
Cc: Matt Turner <mattst88@gmail.com> (reviewed the original patch)
(cherry picked from commit df9dbc03)