At the end of enroll, the image device would put the driver into the
AWAIT_FINGER_ON state and then deactivate the device afterwards. Doing
this adds additional complexity to drivers which would need to handle
both cancellation and normal deactivation from that state.
Only put the device into the AWAIT_FINGER_ON state when we know that
another enroll stage is needed. This avoids the critical state
transition simplifying the driver state machine.
Fixes: #203
Fixes: 689aff0232
7b68344394