ath9k: Clear offchannel state properly

When a pending roc or scan operation is cancelled,
the offchannel operation is cleared, but the offchannel
state in the main scheduler is not cleared. This causes
problems since an active GO will try to process a stale
offchannel request that was deferred earlier. Fix this
by clearing the state when there is no pending offchannel
(roc/scan) operation.

Signed-off-by: Sujith Manoharan <c_manoha@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>