Fix codegen of parameter enumeration arrays

[Martin Sjölund]

Based on code from M.E.D
{{{model M

type E = enumeration(one,two);
parameter E e[E] = {E.one,E.two};
Real r = if e[if time>0.5 then E.one else E.two] == E.one then 1.5 else 2.5;

end M;}}}

The parameter e is stored in the Real parameter array, but should be stored as integer...