nir: fix determining if an addition might overflow for phi sources

nir_addition_might_overflow() expects the parent instruction to be
an alu instr but it might be a phi instr. Fix it by assuming that
the addition might overflow.

This fixes compiler crashes with Horizon Zero Dawn.

No fossils-db changes.

Cc: mesa-stable
Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Daniel Schürmann <daniel@schuermann.dev>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8268>
(cherry picked from commit 0b503d8de96c7006c0fe1c8bfdcd8de02f255992)
2 files changed