ath9k_hw: Fix AR9462 power consumption on idle associated

The HW statemachine is sometimes found stuck in the state
WL_LNA_CTRL_DISABLE when BT is in sleep, which will cause
TX_HOLD always asserted and resmgr stuck in PENDING_TX state

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