Managed to update the usbasp with new firmware. I used a scrap bit of veroboard to put a couple of headers on and wired them pin for pin to create a joiner from my programming cable to the usbasp cable. I loaded up a slightly modified avrisp sketch (changed the reset pin to be D0) onto the leostick. Oddly, I found that if I used one of the usb ports on my laptop for the leostick testing the set up by reading the firmware from the usbasp would randomly hang part way through. When I changed to another USB port the process worked flawlessly. Once I had read the old firmware I uploaded the new firmware to the usbasp which worked fine. Now there are no more messages from avrdude about not being able to set sclk when I upload sketches using the usbasp.