crypto: algif - Change some variable to size_t

Some variable are set as int but store only positive values.
Furthermore there are used in operation/function that wait for unsigned
value.
This patch set them as size_t.

Signed-off-by: LABBE Corentin <clabbe.montjoie@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>