blk-iocost: Correct comment in blk_iocost_init

There is no iocg_pd_init function. The pd_alloc_fn function pointer of
iocost policy is set with ioc_pd_init. Just correct it.
Signed-off-by: Kemeng Shi <shikemeng@huawei.com>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/20221018121932.10792-6-shikemeng@huawei.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-iocost.c

@@ -2882,7 +2882,7 @@ static int blk_iocost_init(struct gendisk *disk)
 	spin_unlock_irq(&ioc->lock);
 
 	/*
-	 * rqos must be added before activation to allow iocg_pd_init() to
+	 * rqos must be added before activation to allow ioc_pd_init() to
 	 * lookup the ioc from q. This means that the rqos methods may get
 	 * called before policy activation completion, can't assume that the
 	 * target bio has an iocg associated and need to test for NULL iocg.