wifi: mwifiex: fix NULL dereference when the AP has HT-cap but no HT-oper

In the Linux kernel, the following vulnerability has been resolved: wifi: mwifiex: fix NULL dereference when the AP has HT-cap but no HT-oper mwifiex_tdls_add_ht_oper() gates its follow-the-AP-bandwidth path on bss_desc->bcn_ht_cap being present, but then dereferences a different pointer, bss_desc->bcn_ht_oper: if (ISSUPP_CHANWIDTH40(priv->adapter->hw_dot_11n_dev_cap) && bss_desc->bcn_ht_cap && ISALLOWED_CHANWIDTH40(bss_desc->bcn_ht_oper->ht_param)) bcn_ht_cap and bcn_ht_oper are populated independently while parsing the associated AP's beacon in mwifiex_update_bss_desc_with_ie(): an AP that advertises an HT Capabilities element but no HT Operation element leaves bcn_ht_cap non-NULL and bcn_ht_oper NULL. Setting up a TDLS link to a peer while associated to such an AP then dereferences the NULL bcn_ht_oper and crashes the kernel. Every other bcn_ht_oper user in the driver NULL-checks it first. Guard on the pointer that is actually dereferenced. Found by 0sec automated security-research tooling (https://0sec.ai).