crypto: s5p-sss - Document the struct s5p_aes_dev

Add kernel-doc to s5p_aes_dev structure.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Reviewed-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>