ath9k_hw: Disable power detector calibration for AR9003

The power detector calibration is disabled because this block
doesn't exist in AR9003 based chips and also parallel
calibration is enabled otherwise the calibration will never stop.

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