test/py: fix the arguments for vfu_dev_irq_state_cb_t (#695)

There is a typo in the arguments for vfu_dev_irq_state_cb_t - fix it in
this patch.

Signed-off-by: Jagannathan Raman <jag.raman@oracle.com>
Reviewed-by: John Levon <john.levon@nutanix.com>