ath9k_hw: Fix ASPM L1 issue for AR9480

Because of not clearing Bit 14 of AR_WA, the ASPM L1 is not
enabled when entering into sleep mode. AR9480 does not need
bit 14 to be set.

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