ntfs: use sb_bdev_nr_blocks

Use the sb_bdev_nr_blocks helper instead of open coding it and clean up
ntfs_fill_super a bit by moving an assignment a little earlier that has
no negative side effects.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Anton Altaparmakov <anton@tuxera.com>
Link: https://lore.kernel.org/r/20211018101130.1838532-29-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

fs/ntfs/super.c

@@ -2772,13 +2772,12 @@ static int ntfs_fill_super(struct super_block *sb, void *opt, const int silent)
 	ntfs_debug("Set device block size to %i bytes (block size bits %i).",
 			blocksize, sb->s_blocksize_bits);
 	/* Determine the size of the device in units of block_size bytes. */
-	if (!i_size_read(sb->s_bdev->bd_inode)) {
+	vol->nr_blocks = sb_bdev_nr_blocks(sb);
+	if (!vol->nr_blocks) {
 		if (!silent)
 			ntfs_error(sb, "Unable to determine device size.");
 		goto err_out_now;
 	}
-	vol->nr_blocks = i_size_read(sb->s_bdev->bd_inode) >>
-			sb->s_blocksize_bits;
 	/* Read the boot sector and return unlocked buffer head to it. */
 	if (!(bh = read_ntfs_boot_sector(sb, silent))) {
 		if (!silent)
@@ -2816,8 +2815,7 @@ static int ntfs_fill_super(struct super_block *sb, void *opt, const int silent)
 			goto err_out_now;
 		}
 		BUG_ON(blocksize != sb->s_blocksize);
-		vol->nr_blocks = i_size_read(sb->s_bdev->bd_inode) >>
-				sb->s_blocksize_bits;
+		vol->nr_blocks = sb_bdev_nr_blocks(sb);
 		ntfs_debug("Changed device block size to %i bytes (block size "
 				"bits %i) to match volume sector size.",
 				blocksize, sb->s_blocksize_bits);