It depends on which sort - as it's flour, it won't have a 'free' allowance, so you can work it out as 1 syn per 20 calories.
I did a quick google and it looks like yam fufu flour is way more synful than plantain fufu flour. (Leemex yam fufu flour appears to be 2000 cals per 100g - which would be 100 syns!!!)