sched/fair: Small cleanup to sched_balance_newidle()

Pull out the !sd check to simplify code.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Tested-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Tested-by: Chris Mason <clm@meta.com>
Link: https://patch.msgid.link/20251107161739.525916173@infradead.org

Author: Peter Zijlstra

kernel/sched/fair.c

@@ -12879,14 +12879,16 @@ static int sched_balance_newidle(struct rq *this_rq, struct rq_flags *rf)
 
 	rcu_read_lock();
 	sd = rcu_dereference_check_sched_domain(this_rq->sd);
+	if (!sd) {
+		rcu_read_unlock();
+		goto out;
+	}
 
 	if (!get_rd_overloaded(this_rq->rd) ||
-	    (sd && this_rq->avg_idle < sd->max_newidle_lb_cost)) {
+	    this_rq->avg_idle < sd->max_newidle_lb_cost) {
 
-		if (sd)
-			update_next_balance(sd, &next_balance);
+		update_next_balance(sd, &next_balance);
 		rcu_read_unlock();
-
 		goto out;
 	}
 	rcu_read_unlock();