crypto: rk3288 - Fix use after free in unprepare

The unprepare call must be carried out before the finalize call
as the latter can free the request.

Fixes: c66c17a0 ("crypto: rk3288 - Remove prepare/unprepare request")
Reported-by: Andrey Skvortsov <andrej.skvortzov@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Reviewed-by: Andrey Skvortsov <andrej.skvortzov@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>