ath9k: support DT ieee80211-freq-limit property to limit channels

The common DT property can be used to limit the available channels
but ath9k has to manually call wiphy_read_of_freq_limits().

I would have put this into ath9k_of_init(). But it didn't work there.
The reason is that in ath9k_of_init() the channels and bands are not yet
registered in the wiphy struct. So there isn't any channel to flag as
disabled.
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20211009212847.1781986-1-chunkeey@gmail.com

drivers/net/wireless/ath/ath9k/init.c

@@ -1094,6 +1094,8 @@ int ath9k_init_device(u16 devid, struct ath_softc *sc,
 		ARRAY_SIZE(ath9k_tpt_blink));
 #endif
 
+	wiphy_read_of_freq_limits(hw->wiphy);
+
 	/* Register with mac80211 */
 	error = ieee80211_register_hw(hw);
 	if (error)