ath9k: Fix ofdm weak signal configuration

The commit, "ath9k_hw: improve ANI processing and rx desensitizing parameters"
removed code setting various phy registers holding threshold values.

This is likely required for OFDM weak signal detection to function
correctly, so add them, but skip AR9462 and AR9565.

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