crypto: hash - Fix handling of small unaligned buffers

If a scatterwalk chain contains an entry with an unaligned offset then
hash_walk_next() will cut off the next step at the next alignment point.

However, if the entry ends before the next alignment point then we a loop,
which leads to a kernel oops.

Fix this by checking whether the next aligment point is before the end of the
current entry.

Signed-off-by: Szilveszter Ördög <slipszi@gmail.com>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>