f2fs: use macro instead of f2fs verity version

Because fsverity_descriptor_location.version is constant,
so use macro for better reading.

Signed-off-by: Jack Qiu <jack.qiu@huawei.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>