[m-rev.] for post-commit review: shut up a C compiler warning

[Julien Fischer]

On Wed, 13 Apr 2022, Zoltan Somogyi wrote:

> I don't why it hasn't been a problem till now, but hard_coded/user_compare
> fails without something like this. It works with my gcc,

It works with the version of GCC on the ROTD host (4.8.5); we probably
don't need to worry about older versions.

> and I *think* it would work with clang, but I have idea with which
> versions. Hence the request for a review.

It's fine with clang 4.2.1, which is from 2017.

Julien.