The leaves appear to be damaged by a stippling insect such as Sycamore plant bug or possibly leafhoppers. Overall the tree looks healthy and is not being negatively affected by the small amount of damage. I would suggest maintaining appropriate moisture as the temperatures increase if damage because intolerable you can look into different types of controls as long as there are insect present.
Please let me know if you have further questions. I have attached a few links that will help you identify the possible insects/bugs.
https://utahpests.usu.edu/ipm/ornamental-pest-guide/arthropods/plant-lace-seed-bugs/sycamore-plant-bug
http://ipm.ucanr.edu/PMG/GARDEN/PLANTS/sycamore.html 
http://hyg.ipm.illinois.edu/article.php?id=539