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.

syntax: glob

.project
*~
*.a
*.orig
.dep
*.Po
autom4te.cache
Makefile
Makefile.in
config.log
stamp-h1
config.status
configure
aclocal.m4



syntax: regexp

\.o$
^iec2c$
^iec2iec$
\.depend$
^stage1_2/iec_bison.cc
^stage1_2/iec_bison.h
^stage1_2/iec_flex.cc
^config/config.h
^test/