The SHA-256 / SHA-224 library functions can't fail, so remove the
useless return value.

Also long as the declarations are being changed anyway, also fix some
parameter names in the declarations to match the definitions.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>