Fix typo in simplify_byte_extract

As the comment says, only simplify when byte_extract_id() matches the current
configuration (and not on a mismatch!).

Author: tautschnig

src/util/simplify_expr.cpp

@@ -1720,7 +1720,7 @@ bool simplify_exprt::simplify_byte_extract(byte_extract_exprt &expr)
   // bytes need to be swapped
   if(offset==0 &&
      base_type_eq(expr.type(), expr.op().type(), ns) &&
-     byte_extract_id()!=expr.id())
+     byte_extract_id() == expr.id())
   {
     exprt tmp=expr.op();
     expr.swap(tmp);