I would usually play it safe and suggest you seek permission from the owner of the logo (that is, the supermarket). But in this case, I don't think that would be necessary. If I've understood you right, this is an ad you created yourself, and you now want to include that ad in your portfolio.
If you had permission to use the logo in the original ad, then that would clearly cover your use of the ad in your portfolio. After all, the whole point of a portfolio is to show the work that you have already done.
If you didn't have permission to use the logo in the original ad, then that in itself is possibly a much bigger problem. Whether or not you use the ad in your portfolio isn't really going to make any difference to that.
If you're still unsure, one option would be to display a small caption under the ad that says something like the XYZ logo is a trademark of the XYZ Company. Personally, I would prefer to do that, rather than blurring out the image, which would detract from the overall appearance of the ad.