If you are interested in coding and aim to work in good corporate firms, then it is suggested that you go for CSE at NIT Calicut. But if you want an IIT tag, you can opt for IIT BHU. But this won't matter much afterward.

So, if you are focused on doing research then Chemical Engineering at IIT BHU will be a good option. You can also learn coding on the sidelines, which might be beneficial if you sit for placements.

The choice of studying in a college pursuing a particular subject is entirely up to you. Check where your strengths and weaknesses lie and then choose accordingly. Both institutes are good in their own way. But it is your hard work and dedication that will prove if CSE or Chemical will be good for you.