rcu: Switch force_qs_rnp() to for_each_leaf_node_cpu_mask()

Currently, force_qs_rnp() uses a for_each_leaf_node_possible_cpu()
loop containing a check of the current CPU's bit in ->qsmask.
This works, but this commit saves three lines by instead using
for_each_leaf_node_cpu_mask(), which combines the functionality of
for_each_leaf_node_possible_cpu() and leaf_node_cpu_bit().  This commit
also replaces the use of the local variable "bit" with rdp->grpmask.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

kernel/rcu/tree.c

@@ -2298,14 +2298,11 @@ static void force_qs_rnp(int (*f)(struct rcu_data *rdp))
 			raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 			continue;
 		}
-		for_each_leaf_node_possible_cpu(rnp, cpu) {
-			unsigned long bit = leaf_node_cpu_bit(rnp, cpu);
-			if ((rnp->qsmask & bit) != 0) {
-				rdp = per_cpu_ptr(&rcu_data, cpu);
-				if (f(rdp)) {
-					mask |= bit;
-					rcu_disable_urgency_upon_qs(rdp);
-				}
+		for_each_leaf_node_cpu_mask(rnp, cpu, rnp->qsmask) {
+			rdp = per_cpu_ptr(&rcu_data, cpu);
+			if (f(rdp)) {
+				mask |= rdp->grpmask;
+				rcu_disable_urgency_upon_qs(rdp);
 			}
 		}
 		if (mask != 0) {