[obv] Fix unused-but-set-variable error [Re: [OB] Fix linux-low.c build error]

[Joel Brobecker]

In this case, I think that the warning was helpful regardless of
the version of GCC that emitted it. However, I did think that Hui's
solution was only sweeping the problem under the carpet and that
did make me uncomfortable.

> Checked in this alternative fix to not break the next nightly builds.

I much prefer your solution which makes it obvious that we decided
to ignore write errors.

-- 
Joel