crypto: rockchip - do not store mode globally

Storing the mode globally does not work if 2 requests are handled in the
same time.
We should store it in a request context.

Fixes: ce0183cb ("crypto: rockchip - switch to skcipher API")
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>