FTL: Fix SmallMap<K, V, 0>::try_emplace

SmallVector<T, N>::emplace_back returns a reference, whereas
SmallVector<T, 0>::emplace_back returns an iterator (because
its API must be compatible with StaticVector).

Bug: 185536303
Test: ftl_test
Change-Id: I6bdcd983c0bb2d2a326f79906997f85e89d7df44
2 files changed