avrdude: auto set sck period (because given equals null)
avrdude: warning: cannot set sck period. please check for usbasp firmware update.
This output indicates your USBasp does not support the -B option. It may be possible to upgrade your programmer firmware to be able to support that option. If you tell us what kind of USBasp you have then I may be able to help you upgrade it.
If you had set the CKOUT fuse option, then the system clock can be measured at the output CLKO on pin 9.
What low clock fuse setting did you use?