crypto: caam - check zero-length input

Check zero-length input, for skcipher algorithm, to solve the extra
tests. This is a valid operation, therefore the API will return no error.

Signed-off-by: Iuliana Prodan <iuliana.prodan@nxp.com>
Reviewed-by: Horia Geanta <horia.geanta@nxp.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>