fix compilation error about missing braces

IEC_TIMESPEC has two fields tv_sec and tv_nsec.

Compilation error:
./build/POUS.c:600:45: error: missing braces around initializer [-Werror=missing-braces]
static const STEP temp_step = {{0, 0}, 0, {0, 0}};
^
compilation terminated due to -Wfatal-errors.

Source: matiec
Section: devel
Priority: standard
Maintainer: edouard <edouard.tisserant@gmail.com>
Build-Depends: debhelper (>= 5), bison, flex
Standards-Version: 3.7.2

Package: matiec
Architecture: any
Depends: ${shlibs:Depends}, ${misc:Depends}
Description: The IEC to ANSI-C compiler
 Compiles ST/IL/SFC code into ANSI-C code