Probably commemorates Frederick Blackwood, 1st Marquis of Dufferin and Ava, or one of his family. See Ava Street for further details.
The Marquess of Dufferin and Ava was appointed Lord Warden of the Cinque Ports with the official residence as Walmer in Kent - in 1891. A very symbolically important honour within the UK. This prestigious appointment is recognised in the naming of several streets off the Ormeau Road.
"The city surveyor was authorised to approve the following names for new streets: ... Ava Crescent and Sunnyside Park for New Streets of Sunnyside St on the property of Mr JH Dowling." (27th June 1939).