Bug fix in SIMD result detection.

Rationale:
Only 2-way phis are currently used in reductions
to carry SIMD results. Note that this will go away
when we introduce proper SIMD types.

Note:
So far I have not been able to make a small regression
test for this. Any pointers on how to set up a catch phi?

Test: test-art-host,target

Bug: b/77725987
Change-Id: I8f8b2dbec35e906878b7f7ed62690c3234db4211