tcm_fc: rcu_deref outside rcu lock/unlock section

Use rcu_dereference_protected in order to prevent lockdep
complaint. Sequel of the patch 863555be

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Denis Efremov <[e-mail]>
Acked-by: Mark D. Rustad <[e-mail]>
Signed-off-by: Nicholas Bellinger <[e-mail]>

drivers/target/tcm_fc/tfc_sess.c

···
 	struct ft_tport *tport;
 
 	mutex_lock(&ft_lport_lock);
-	tport = rcu_dereference(rdata->local_port->prov[FC_TYPE_FCP]);
+	tport = rcu_dereference_protected(rdata->local_port->prov[FC_TYPE_FCP],
+					  lockdep_is_held(&ft_lport_lock));
+
 	if (!tport) {
 		mutex_unlock(&ft_lport_lock);
 		return;