cfq-iosched: simplify control flow in cfq_get_queue()

cfq_get_queue()'s control flow looks like the following.

	async_cfqq = NULL;
	cfqq = NULL;

	if (!is_sync) {
		...
		async_cfqq = ...;
		cfqq = *async_cfqq;
	}

	if (!cfqq)
		cfqq = ...;

	if (!is_sync && !(*async_cfqq))
		...;

The only thing the local variable init, the second if, and the
async_cfqq test in the third if achieves is to skip cfqq creation and
installation if *async_cfqq was already non-NULL.  This is needlessly
complicated with different tests examining the same condition.
Simplify it to the following.

	if (!is_sync) {
		...
		async_cfqq = ...;
		cfqq = *async_cfqq;
		if (cfqq)
			goto out;
	}

	cfqq = ...;

	if (!is_sync)
		...;
 out:
Signed-off-by: NTejun Heo <tj@kernel.org>
Acked-by: NJeff Moyer <jmoyer@redhat.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Arianna Avanzini <avanzini.arianna@gmail.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

block/cfq-iosched.c

@@ -3731,8 +3731,8 @@ cfq_get_queue(struct cfq_data *cfqd, bool is_sync, struct cfq_io_cq *cic,
 {
 	int ioprio_class = IOPRIO_PRIO_CLASS(cic->ioprio);
 	int ioprio = IOPRIO_PRIO_DATA(cic->ioprio);
-	struct cfq_queue **async_cfqq = NULL;
-	struct cfq_queue *cfqq = NULL;
+	struct cfq_queue **async_cfqq;
+	struct cfq_queue *cfqq;
 
 	if (!is_sync) {
 		if (!ioprio_valid(cic->ioprio)) {
@@ -3742,19 +3742,20 @@ cfq_get_queue(struct cfq_data *cfqd, bool is_sync, struct cfq_io_cq *cic,
 		}
 		async_cfqq = cfq_async_queue_prio(cfqd, ioprio_class, ioprio);
 		cfqq = *async_cfqq;
+		if (cfqq)
+			goto out;
 	}
 
-	if (!cfqq)
-		cfqq = cfq_find_alloc_queue(cfqd, is_sync, cic, bio, gfp_mask);
+	cfqq = cfq_find_alloc_queue(cfqd, is_sync, cic, bio, gfp_mask);
 
 	/*
 	 * pin the queue now that it's allocated, scheduler exit will prune it
 	 */
-	if (!is_sync && !(*async_cfqq)) {
+	if (!is_sync) {
 		cfqq->ref++;
 		*async_cfqq = cfqq;
 	}
-
+out:
 	cfqq->ref++;
 	return cfqq;
 }