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/chan.c b/net/mac80211/chan.c
index 32be11e..5b24740 100644
--- a/net/mac80211/chan.c
+++ b/net/mac80211/chan.c
@@ -11,7 +11,7 @@
 {
 	struct ieee80211_sub_if_data *sdata;
 
-	WARN_ON(!mutex_is_locked(&local->iflist_mtx));
+	lockdep_assert_held(&local->iflist_mtx);
 
 	list_for_each_entry(sdata, &local->interfaces, list) {
 		if (sdata == ignore)