#4342: few missing malloc return checks and free in error paths

ossl_hmac_cleanup, pkey_hmac_cleanup:
 - allow to invoke with NULL data
 - using EVP_PKEY_CTX_[get|set]_data

EVP_DigestInit_ex:
 - remove additional check for ‘type’ and doing clear free instead of
free

Reviewed-by: Rich Salz <rsalz@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>