CIF to PLC generates wrong assignment syntax for some temporary variables for multi-assignments of internal user-defined functions

See tests/cif2plc/int_funcs_iec/func_f3.plcfunc on line 21 and 22:

fvar_f3_x = tmp0;
fvar_f3_y = tmp1;

Should be

fvar_f3_x := tmp0;
fvar_f3_y := tmp1;