ath10k: clean up monitor start code

Remove useless code that was causing WARN_ON when
a 80MHz+ vif entered promiscuous mode or monitor
interface was started.

The channel mode is already computed by
chan_to_phymode().
Signed-off-by: Michal Kazior <michal.kazior@tieto.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>

drivers/net/wireless/ath/ath10k/mac.c

@@ -503,13 +503,10 @@ static int ath10k_monitor_start(struct ath10k *ar, int vdev_id)
 {
 	struct ieee80211_channel *channel = ar->hw->conf.chandef.chan;
 	struct wmi_vdev_start_request_arg arg = {};
-	enum nl80211_channel_type type;
 	int ret = 0;
 
 	lockdep_assert_held(&ar->conf_mutex);
 
-	type = cfg80211_get_chandef_type(&ar->hw->conf.chandef);
-
 	arg.vdev_id = vdev_id;
 	arg.channel.freq = channel->center_freq;
 	arg.channel.band_center_freq1 = ar->hw->conf.chandef.center_freq1;