ath9k_hw: Assign default xlna config for AR9485

commit 30d5b709da23f4ab9836c7f66d2d2e780a69cf12 upstream.

For AR9485 boards with XLNA, the default gpio config
is not set correctly, fix this.

Signed-off-by: Sujith Manoharan <c_manoha@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>