Ha....I learned something new today! There is a Yorkshire Terrier Puppy and Adult food! According to the chart you should feed the puppy variety for a few more months until the age of 9 months old.
Yorkshire Terrier Puppy / BREED HEALTH NUTRITION? / Dog Products / Products / Products / Home Royal Canin USA - Royal Canin
I do not see a Maltese food and really I don't see why you couldn't feed the Yorkie food. They also have XS and small kibble. I did notice their coats looked very shiny when feeding the Yorkie formula. So to answer your question I think you should stick with the Yorkie puppy and then switch over to the adult formula.