ath9k: Fix bug in scan termination

A full HW reset needs to be done on termination of a scan run.
Not setting SC_OP_FULL_RESET resulted in doing a
fast channel change.

Cc: stable@kernel.org
Signed-off-by: Sujith <Sujith.Manoharan@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>