ath9k: Reduce the frequency of PA offset calibration

PA calibration need not be done if the offset is not varying.
The current logic does PA calibration even if the offset is the
same.

Signed-off-by: Sujith <Sujith.Manoharan@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
3 files changed