That's just a warning. The sketch should have been loaded.
I have been using the Alpha firmware on several USBasp's and it works great on anything I have tried.
""usbasp-v1.06-alpha-2016-04-17-atmega8.hex" from petervh/bperrybap solves all these issues. myself and friends been using it for couple months now. big improvement. more info and other versions: https://github.com/bperrybap/usbasp/tree/1.06-alpha."