ath9k: Enable D3/L1 ASPM fix for AR9462

AR9462 requires this HW fix for ASPM to work properly.
Also, since WARegVal is used only for the AR8003 family,
use AR_SREV_9300_20_OR_LATER.

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