ath9k: Stop ANI when doing a reset

The MIB counters are disabled when doing a chip reset.
Since ANI depends on the MIB registers for its operation, relying
on the contents of said registers during HW reset results in sub-optimal
performance.

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