ath9k_hw: Fix fixed antenna for AR9462

When the RX chainmask is set to 0x2 for AR9462, certain values
from chain1 have to be programmed for chain0 also.

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