cfg80211/mac80211: use lockdep_assert_held

Instead of using a WARN_ON(!mutex_is_locked())
use lockdep_assert_held() which compiles away
completely when lockdep isn't enabled, and
also is a more accurate assertion since it
checks that the current thread is holding the
mutex.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/net/mac80211/key.c b/net/mac80211/key.c
index 3570f8c..6a63d1a 100644
--- a/net/mac80211/key.c
+++ b/net/mac80211/key.c
@@ -49,7 +49,7 @@
 
 static void assert_key_lock(struct ieee80211_local *local)
 {
-	WARN_ON(!mutex_is_locked(&local->key_mtx));
+	lockdep_assert_held(&local->key_mtx);
 }
 
 static struct ieee80211_sta *get_sta_for_key(struct ieee80211_key *key)