crypto: sun4i-ss - Fix 64-bit size_t warnings on sun4i-ss-hash.c

If you try to compile this driver on a 64-bit platform then you
will get warnings because it mixes size_t with unsigned int which
only works on 32-bit.

This patch fixes all of the warnings on sun4i-ss-hash.c.
Signed-off-by: Corentin Labbe <clabbe.montjoie@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>