ath9k_hw: Program filter coefficients correctly

2484 Mhz (Japan) usage requires filter coefficients to
be programmed in the CCK TX FIR registers. This is required
for AR9331, AR9485 and AR9462. Fix this and also remove
a few useless macros and a duplicate variable.

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