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/mlme.c b/net/mac80211/mlme.c
index 0cb822c..bfb0eab 100644
--- a/net/mac80211/mlme.c
+++ b/net/mac80211/mlme.c
@@ -92,7 +92,7 @@
 /* utils */
 static inline void ASSERT_MGD_MTX(struct ieee80211_if_managed *ifmgd)
 {
-	WARN_ON(!mutex_is_locked(&ifmgd->mtx));
+	lockdep_assert_held(&ifmgd->mtx);
 }
 
 /*