Good catch on the double meaning! Dickens was very intentional with his wording, so we have to assume that this was intended as well.
On the surface, we take the word "stave" at face value -- as a portion of a song (like a stanza of a poem). This matches the title of the work. If the entire work is a song or a "carol," then it would make sense that the individual parts that comprise it would be known as staves.
However, as you astutely point out, to stave something off is to keep something from happening, or to at least delay it. No doubt the ghosts are trying to stave off Scrooge's potentially meaningless life by showing him his past, present, and future.