fs: use bdev_nr_bytes instead of open coding it in blkdev_max_block

Use the proper helper to read the block device size.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Link: https://lore.kernel.org/r/20211018101130.1838532-10-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

fs/buffer.c

@@ -878,7 +878,7 @@ link_dev_buffers(struct page *page, struct buffer_head *head)
 static sector_t blkdev_max_block(struct block_device *bdev, unsigned int size)
 {
 	sector_t retval = ~((sector_t)0);
-	loff_t sz = i_size_read(bdev->bd_inode);
+	loff_t sz = bdev_nr_bytes(bdev);
 
 	if (sz) {
 		unsigned int sizebits = blksize_bits(size);