Literally, διδόναι is the present active infinitive (to give). However, in this verse it has the meaning of keep giving because next verse says that this servant will be blessed if his master will find him so doing when he comes.
So, keep giving for the period of the master's absence. But I think "to give" has the meaning of an ongoing action as well.
"They told me to pay attention"
To pay, here is a continuous action, right? I pay attention all the time even now.