ath9k_hw: Fix a reset failure on AR9382 (2x2).

AR9382 needs to be configured for the correct chain mask before
running AGC/TxIQ caliberation. Otherwise reset would fail.

Signed-off-by: Senthil Balasubramanian <senthilkumar@atheros.com>
Signed-off-by: Vasanthakumar Thiagarajan <vasanth@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>