crypto: rockchip - use a rk_crypto_info variable instead of lot of indirection

Instead of using lot of ctx->dev->xx indirections, use an intermediate
variable for rk_crypto_info.
This will help later, when 2 different rk_crypto_info would be used.

Reviewed-by: John Keeping <john@metanate.com>
Signed-off-by: Corentin Labbe <clabbe@baylibre.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>