wifi: cfg80211: address several kerneldoc warnings

wifi: cfg80211: address several kerneldoc warnings

include/net/cfg80211.h includes a number of kerneldoc entries for struct
members that do not exist, leading to these warnings:

  ./include/net/cfg80211.h:3192: warning: Excess struct member 'band_pref' description in 'cfg80211_bss_selection'
  ./include/net/cfg80211.h:3192: warning: Excess struct member 'adjust' description in 'cfg80211_bss_selection'
  ./include/net/cfg80211.h:6181: warning: Excess struct member 'bssid' description in 'wireless_dev'
  ./include/net/cfg80211.h:6181: warning: Excess struct member 'beacon_interval' description in 'wireless_dev'
  ./include/net/cfg80211.h:7299: warning: Excess struct member 'bss' description in 'cfg80211_rx_assoc_resp_data'

Remove and/or repair each entry to address the warnings and ensure a proper
docs build for the affected structures.

Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Link: https://msgid.link/87plz1g2sc.fsf@meer.lwn.net
Signed-off-by: Johannes Berg <johannes.berg@intel.com>