Remove "if (auto ret = " treated as unused by some compilers

It's not good form to have a variable that's created and used only once
in the same line anyway, so the compilers that flag it are probably in
the right.

Test: netd_benchmark
Bug: 29748723
Change-Id: Idfa51a8ffb11b70f18a3c4afafc59f1910f48a83