ath9k_hw: Fix PAPRD retraining for AR9485

Retraining of PAPRD based on agc2_pwr is required for
chips other than AR9485.

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