rcu: Update from rcu_expedited variable to rcu_gp_is_expedited()

This commit updates open-coded tests of the rcu_expedited variable
to instead use rcu_gp_is_expedited().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 0a571e9..63726b7 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -585,7 +585,7 @@
 			   "Illegal synchronize_rcu() in RCU read-side critical section");
 	if (!rcu_scheduler_active)
 		return;
-	if (rcu_expedited)
+	if (rcu_gp_is_expedited())
 		synchronize_rcu_expedited();
 	else
 		wait_rcu_gp(call_rcu);