crypto: shash - fold shash_digest_unaligned() into crypto_shash_digest()

Fold shash_digest_unaligned() into its only remaining caller.  Also,
avoid a redundant check of CRYPTO_TFM_NEED_KEY by replacing the call to
crypto_shash_init() with shash->init(desc).  Finally, replace
shash_update_unaligned() + shash_final_unaligned() with
shash_finup_unaligned() which does exactly that.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>