ath11k: fix a double free and a memory leak

clang static analyzer reports this problem

mac.c:6204:2: warning: Attempt to free released memory
        kfree(ar->mac.sbands[NL80211_BAND_2GHZ].channels);
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The channels pointer is allocated in ath11k_mac_setup_channels_rates()
When it fails midway, it cleans up the memory it has already allocated.
So the error handling needs to skip freeing the memory.

There is a second problem.
ath11k_mac_setup_channels_rates(), allocates 3 channels. err_free
misses releasing ar->mac.sbands[NL80211_BAND_6GHZ].channels

Fixes: d5c65159 ("ath11k: driver for Qualcomm IEEE 802.11ax devices")
Signed-off-by: Tom Rix <trix@redhat.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200906212625.17059-1-trix@redhat.com

drivers/net/wireless/ath/ath11k/mac.c

@@ -6089,7 +6089,7 @@ static int __ath11k_mac_register(struct ath11k *ar)
 	ret = ath11k_mac_setup_channels_rates(ar,
 					      cap->supported_bands);
 	if (ret)
-		goto err_free;
+		goto err;
 
 	ath11k_mac_setup_ht_vht_cap(ar, cap, &ht_cap);
 	ath11k_mac_setup_he_cap(ar, cap);
@@ -6203,7 +6203,9 @@ static int __ath11k_mac_register(struct ath11k *ar)
 err_free:
 	kfree(ar->mac.sbands[NL80211_BAND_2GHZ].channels);
 	kfree(ar->mac.sbands[NL80211_BAND_5GHZ].channels);
+	kfree(ar->mac.sbands[NL80211_BAND_6GHZ].channels);
 
+err:
 	SET_IEEE80211_DEV(ar->hw, NULL);
 	return ret;
 }