ath9k: fix QCA9561 XLNA rxgain initial

A small bugfix for commit ede6a5e7 ("ath9k: Add QCA956x HW support").
I guess I would have skipped renaming (that initial QCA956x commit has
been there already for almost a year with the "5g" in the name) and move
the call outside AR_SREV_9462_20_OR_LATER() to make it reachable.

Signed-off-by: Miaoqing Pan <miaoqing@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>