ath9k_hw: Fix STA connection issues with AR9380 (XB113).

XB113 (AR9380) 3x3 SB 5G only cards were failing to connect to APs
due to incorrect xpabiaslevel configuration. fix it.

Cc: stable@kernel.org
Cc: Ray Li <ray.li@greenwavereality.com>
Cc: Kathy Giori <kathy.giori@atheros.com>
Cc: Aeolus Yang <aeolus.yang@atheros.com>
Cc: compat@orbit-lab.org
Signed-off-by: Senthil Balasubramanian <senthilkumar@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>