[otbn] Fix idle logic
[otbn] Fix idle logic

We are idle if we aren't running (~ busy_q) and also aren't being told
to start (~ start).

Signed-off-by: Rupert Swarbrick <290093e2ad2515ed2f14d749293c8cf8e02ca274@lowrisc.org>

lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan