wifi: mac80211: fix maybe-unused warning

In ieee80211_lookup_key, the variable named `local` is unused if
compiled without lockdep, getting this warning:

net/mac80211/cfg.c: In function ‘ieee80211_lookup_key’:
net/mac80211/cfg.c:542:26: error: unused variable ‘local’ [-Werror=unused-variable]
  struct ieee80211_local *local = sdata->local;
                          ^~~~~

Fix it with __maybe_unused.

Fixes: 8cbf0c2a ("wifi: mac80211: refactor some key code")
Signed-off-by: Íñigo Huguet <ihuguet@redhat.com>
Link: https://lore.kernel.org/r/20221111153622.29016-1-ihuguet@redhat.comSigned-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/cfg.c

@@ -576,7 +576,7 @@ static struct ieee80211_key *
 ieee80211_lookup_key(struct ieee80211_sub_if_data *sdata, int link_id,
 		     u8 key_idx, bool pairwise, const u8 *mac_addr)
 {
-	struct ieee80211_local *local = sdata->local;
+	struct ieee80211_local *local __maybe_unused = sdata->local;
 	struct ieee80211_link_data *link = &sdata->deflink;
 	struct ieee80211_key *key;