ath9k_hw: Fix wrong peak detector DC offset

An issue is reported in AR9462 & AR9565 that NF_cal_not_done is
not observed when HW peak detector calibration is disabled. At that
state, the HW is stuck at NF calibration which prevents tx output.
The root cause is wrong peak detector offset calibrated by HW. To
resolve this issue, peak detector calibration is done manually by SW
for AR9462 and AR9565.

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