This also makes the dummy scatterlist in mv_hash_final() needless, so
drop it.

XXX: should this routine be made pulicly available? There are probably
other users with their own implementations.
Signed-off-by: NPhil Sutter <phil.sutter@viprinet.com>
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>