crypto: sha-mb - Fix total_len for correct hash when larger than 512MB

Current multi-buffer hash implementations have a restriction on the total
length of a hash job to 512MB. Hashing larger buffers will result in an
incorrect hash. This extends the limit to 2^62 - 1.

Signed-off-by: Greg Tucker <greg.b.tucker@intel.com>
Acked-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>