nvmet: use bdev_nr_bytes instead of open coding it

Use the proper helper to read the block device size.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NKees Cook <keescook@chromium.org>
Reviewed-by: NChaitanya Kulkarni <kch@nvidia.com>
Link: https://lore.kernel.org/r/20211018101130.1838532-8-hch@lst.deSigned-off-by: NJens Axboe <axboe@kernel.dk>

drivers/nvme/target/io-cmd-bdev.c

@@ -87,7 +87,7 @@ int nvmet_bdev_ns_enable(struct nvmet_ns *ns)
 		ns->bdev = NULL;
 		return ret;
 	}
-	ns->size = i_size_read(ns->bdev->bd_inode);
+	ns->size = bdev_nr_bytes(ns->bdev);
 	ns->blksize_shift = blksize_bits(bdev_logical_block_size(ns->bdev));
 
 	ns->pi_type = 0;
@@ -108,7 +108,7 @@ int nvmet_bdev_ns_enable(struct nvmet_ns *ns)
 
 void nvmet_bdev_ns_revalidate(struct nvmet_ns *ns)
 {
-	ns->size = i_size_read(ns->bdev->bd_inode);
+	ns->size = bdev_nr_bytes(ns->bdev);
 }
 
 u16 blk_to_nvme_status(struct nvmet_req *req, blk_status_t blk_sts)