ath9k: Clear NoA schedule properly

When an active context transitions to inactive
state, the NoA schedule needs to be removed
for the context that has beaconing enabled.
Not doing this will affect p2p clients.

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