mac80211: fix potential null pointer dereference

he_op is being dereferenced before it is null checked, hence there
is a potential null pointer dereference.

Fix this by moving the pointer dereference after he_op has been
properly null checked.

Notice that, currently, he_op is already being null checked before
calling this function at 4593:

4593	if (!he_oper ||
4594	    !ieee80211_verify_sta_he_mcs_support(sband, he_oper))
4595		ifmgd->flags |= IEEE80211_STA_DISABLE_HE;

but in case ieee80211_verify_sta_he_mcs_support is ever called
without verifying he_oper is not null, we will end up having a
null pointer dereference. So, we better don't take any chances.

Addresses-Coverity-ID: 1470068 ("Dereference before null check")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/mlme.c

@@ -4458,12 +4458,14 @@ ieee80211_verify_sta_he_mcs_support(struct ieee80211_supported_band *sband,
 {
 	const struct ieee80211_sta_he_cap *sta_he_cap =
 		ieee80211_get_he_sta_cap(sband);
-	u16 ap_min_req_set = le16_to_cpu(he_op->he_mcs_nss_set);
+	u16 ap_min_req_set;
 	int i;
 
 	if (!sta_he_cap || !he_op)
 		return false;
 
+	ap_min_req_set = le16_to_cpu(he_op->he_mcs_nss_set);
+
 	/* Need to go over for 80MHz, 160MHz and for 80+80 */
 	for (i = 0; i < 3; i++) {
 		const struct ieee80211_he_mcs_nss_supp *sta_mcs_nss_supp =