Remove C99 syntax from fakenect.c

Recent commit a05075a1bda356a79c3eeddcc4eab1ac20008425 uses C99 syntax
on line 101 of fakenect.c:

    for (int c = /* snip */

However, the build system compiles (at least on my machine) using C89,
causing the build to fail. Moving the declaration of int c to the top
of the function solves the problem.