wifi: mac80211: Add missing return value documentation

wifi: mac80211: Add missing return value documentation

kernel-doc is reporting some warnings, so fix them:

% scripts/kernel-doc -Wall -Werror -none include/net/mac80211.h
include/net/mac80211.h:2056: warning: No description found for return value of 'wdev_to_ieee80211_vif'
include/net/mac80211.h:2066: warning: No description found for return value of 'ieee80211_vif_to_wdev'
include/net/mac80211.h:5603: warning: No description found for return value of 'ieee80211_beacon_cntdwn_is_complete'
include/net/mac80211.h:5968: warning: No description found for return value of 'ieee80211_gtk_rekey_add'
include/net/mac80211.h:6350: warning: No description found for return value of 'ieee80211_find_sta_by_link_addrs'
include/net/mac80211.h:6478: warning: No description found for return value of 'ieee80211_txq_airtime_check'
include/net/mac80211.h:6981: warning: No description found for return value of 'rate_control_set_rates'
include/net/mac80211.h:7142: warning: No description found for return value of 'ieee80211_tx_prepare_skb'
include/net/mac80211.h:7156: warning: No description found for return value of 'ieee80211_parse_tx_radiotap'
include/net/mac80211.h:7277: warning: No description found for return value of 'ieee80211_tx_dequeue'
include/net/mac80211.h:7292: warning: No description found for return value of 'ieee80211_tx_dequeue_ni'
include/net/mac80211.h:7324: warning: No description found for return value of 'ieee80211_next_txq'
include/net/mac80211.h:7405: warning: No description found for return value of 'ieee80211_txq_may_transmit'
include/net/mac80211.h:7466: warning: No description found for return value of 'ieee80211_calc_rx_airtime'
include/net/mac80211.h:7480: warning: No description found for return value of 'ieee80211_calc_tx_airtime'
include/net/mac80211.h:7528: warning: No description found for return value of 'ieee80211_is_tx_data'
include/net/mac80211.h:7562: warning: No description found for return value of 'ieee80211_set_active_links'
17 warnings as Errors

Signed-off-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Tested-by: Randy Dunlap <rdunlap@infradead.org>
Link: https://msgid.link/20240329-mac80211-kdoc-retval-v1-2-5e4d1ad6c250@quicinc.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>