sha256: fix verify failure

sha256: fix verify failure

After the checksumming update, it's required that we call the
_final() to get consistent checksums between data generation
and data verification. Seems to only affect sha256, but we should
do it for sha1 and md5 too.

Fixes: f99d67f932ab
Signed-off-by: Jens Axboe <axboe@fb.com>