n64cart: convert bi_disk to bi_bdev->bd_disk fix build

My kernel robot report below:

  drivers/block/n64cart.c: In function ‘n64cart_submit_bio’:
  drivers/block/n64cart.c:91:26: error: ‘struct bio’ has no member named ‘bi_disk’
     91 |  struct device *dev = bio->bi_disk->private_data;
        |                          ^~
    CC      drivers/slimbus/qcom-ctrl.o
    CC      drivers/auxdisplay/hd44780.o
    CC      drivers/watchdog/watchdog_core.o
    CC      drivers/nvme/host/fault_inject.o
    AR      drivers/accessibility/braille/built-in.a
  make[2]: *** [scripts/Makefile.build:288: drivers/block/n64cart.o] Error 1

Fixes: 309dca30 ("block: store a block_device pointer in struct bio");
Reported-by: Nk2ci <kernel-bot@kylinos.cn>
Signed-off-by: NJackie Liu <liuyun01@kylinos.cn>
Reviewed-by: NChaitanya Kulkarni <kch@nvidia.com>
Link: https://lore.kernel.org/r/20220321071216.1549596-1-liu.yun@linux.devSigned-off-by: NJens Axboe <axboe@kernel.dk>

drivers/block/n64cart.c

@@ -88,7 +88,7 @@ static void n64cart_submit_bio(struct bio *bio)
 {
 	struct bio_vec bvec;
 	struct bvec_iter iter;
-	struct device *dev = bio->bi_disk->private_data;
+	struct device *dev = bio->bi_bdev->bd_disk->private_data;
 	u32 pos = bio->bi_iter.bi_sector << SECTOR_SHIFT;
 
 	bio_for_each_segment(bvec, bio, iter) {