pstore/blk: use bdev_nr_bytes instead of open coding it

Use the proper helper to read the block device size.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20211018101130.1838532-22-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

fs/pstore/blk.c

@@ -205,7 +205,6 @@ static ssize_t psblk_generic_blk_write(const char *buf, size_t bytes,
 static int __register_pstore_blk(struct pstore_device_info *dev,
 				 const char *devpath)
 {
-	struct inode *inode;
 	int ret = -ENODEV;
 
 	lockdep_assert_held(&pstore_blk_lock);
@@ -217,14 +216,13 @@ static int __register_pstore_blk(struct pstore_device_info *dev,
 		goto err;
 	}
 
-	inode = file_inode(psblk_file);
-	if (!S_ISBLK(inode->i_mode)) {
+	if (!S_ISBLK(file_inode(psblk_file)->i_mode)) {
 		pr_err("'%s' is not block device!\n", devpath);
 		goto err_fput;
 	}
 
-	inode = I_BDEV(psblk_file->f_mapping->host)->bd_inode;
-	dev->zone.total_size = i_size_read(inode);
+	dev->zone.total_size =
+		bdev_nr_bytes(I_BDEV(psblk_file->f_mapping->host));
 
 	ret = __register_pstore_device(dev);
 	if (ret)