Ensure HMAC key gets cleansed after use

aesni_cbc_hmac_sha256_ctrl() and aesni_cbc_hmac_sha1_ctrl() cleanse the
HMAC key after use, but static int rc4_hmac_md5_ctrl() doesn't.

Fixes an OCAP Audit issue.

Reviewed-by: Andy Polyakov <appro@openssl.org>