ath9k: avoid ANI restart if no trigger

Fixes commit 54da20d8

 ("ath9k_hw: improve ANI processing and rx desensitizing parameters")

Call ath9k_ani_restart() only when the phy error rate reach the
ANI immunity threshold. Sync the logic with internal code base.

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