crypto: fixup scrypt regressions

Fixes a handful of regressions in scrypt support following
the refactor.

Fixes: https://github.com/nodejs/node/issues/35815

PR-URL: https://github.com/nodejs/node/pull/35821


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>