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.

FUNCTION_BLOCK HYSTERESIS
    (* Boolean hysteresis on difference *)
    (* of REAL inputs, XIN1 - XIN2      *)
  VAR_INPUT XIN1, XIN2, EPS : REAL; END_VAR
  VAR_OUTPUT Q : BOOL := 0; END_VAR
  IF Q THEN IF XIN1 < (XIN2 - EPS) THEN Q := 0; END_IF ;
  ELSIF XIN1 > (XIN2 + EPS) THEN Q := 1 ;
  END_IF ;
END_FUNCTION_BLOCK