lib/crypto: sha256: Propagate sha256_block_state type to implementations

The previous commit made the SHA-256 compression function state be
strongly typed, but it wasn't propagated all the way down to the
implementations of it.  Do that now.

Acked-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20250630160645.3198-8-ebiggers@kernel.org


Signed-off-by: Eric Biggers <ebiggers@kernel.org>