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/sta_info.c b/net/mac80211/sta_info.c
index e356ff8..44e10a9 100644
--- a/net/mac80211/sta_info.c
+++ b/net/mac80211/sta_info.c
@@ -280,7 +280,7 @@
 	unsigned long flags;
 	int err = 0;
 
-	WARN_ON(!mutex_is_locked(&local->sta_mtx));
+	lockdep_assert_held(&local->sta_mtx);
 
 	/* notify driver */
 	if (sdata->vif.type == NL80211_IFTYPE_AP_VLAN)