We were computing the size of the import buffer based on the digest size
but the 318 and 224 byte variants use 512 and 256 bytes internal state
sizes respectfully, thus causing the import buffer to overrun.

Fix it by using the right sizes.
Signed-off-by: Gilad Ben-Yossef <gilad@benyossef.com>
Cc: stable@vger.kernel.org # v4.19+
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>