Optimize the mterp field setter.

Same as getters. FindFieldFast does ligth-weight access checks
which are not necessary when running under mterp.

This reduces the overhead of non-quickened code from 1.35x to 1.25x.
(golem benchmarks on arm64 with quickening manually disabled)

Test: profiled benchmark locally on host
Change-Id: I6ccb45ee28de0a395798448e8e5d181ea11c3876