ath9k: fix misleading indent

Fixes smatch warning:

ath9k_vif_iter_set_beacon() warn if statement not indented

Signed-off-by: Bob Copeland <me@bobcopeland.com>
Reviewed-by: Julian Calaby <julian.calaby@gmail.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>