iwlwifi: fix locking assertions

spin_is_locked() can return zero on some (UP?)
configurations because locks don't exist, and
that causes an endless amount of warnings. Use
lockdep_assert_held() instead, which has two
advantages:
 1) it verifies the current task is holding
    the lock or mutex
 2) it compiles away completely when lockdep
    is not enabled

Cc: stable@kernel.org [2.6.34+, maybe only parts of patch]
Reported-by: Thomas Meyer <thomas@m3y3r.de>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/iwlwifi/iwl-agn-tx.c b/drivers/net/wireless/iwlwifi/iwl-agn-tx.c
index ecb953f..d04502d 100644
--- a/drivers/net/wireless/iwlwifi/iwl-agn-tx.c
+++ b/drivers/net/wireless/iwlwifi/iwl-agn-tx.c
@@ -1117,7 +1117,7 @@
 	u8 *addr = priv->stations[sta_id].sta.sta.addr;
 	struct iwl_tid_data *tid_data = &priv->stations[sta_id].tid[tid];
 
-	WARN_ON(!spin_is_locked(&priv->sta_lock));
+	lockdep_assert_held(&priv->sta_lock);
 
 	switch (priv->stations[sta_id].tid[tid].agg.state) {
 	case IWL_EMPTYING_HW_QUEUE_DELBA: