mt76: mt7915: take RCU read lock when calling ieee80211_bss_get_elem()

As ieee80211_bss_get_elem() derefences an RCU to return ie, both
the call to this function and any operation on this variable need
protection by the RCU read lock.
Signed-off-by: Ryder Lee <ryder.lee@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>

drivers/net/wireless/mediatek/mt76/mt7915/mcu.c

@@ -923,12 +923,15 @@ static void mt7915_check_he_obss_narrow_bw_ru_iter(struct wiphy *wiphy,
 	struct mt7915_he_obss_narrow_bw_ru_data *data = _data;
 	const struct element *elem;
 
+	rcu_read_lock();
 	elem = ieee80211_bss_get_elem(bss, WLAN_EID_EXT_CAPABILITY);
 
 	if (!elem || elem->datalen <= 10 ||
 	    !(elem->data[10] &
 	      WLAN_EXT_CAPA10_OBSS_NARROW_BW_RU_TOLERANCE_SUPPORT))
 		data->tolerated = false;
+
+	rcu_read_unlock();
 }
 
 static bool mt7915_check_he_obss_narrow_bw_ru(struct ieee80211_hw *hw,