Allow oversized buffers for provider cipher IV fetch

Allow oversized buffers for provider cipher IV fetch

When we're fetching an IV, there's no need to enforce that the
provided buffer is exactly the same size as the IV we want to
write into it.  This might happen, for example, when
EVP_CIPHER_CTX_iv_noconst() passes sizeof(ctx->iv) (that is,
EVP_MAX_IV_LENGTH) for an AES-GCM cipher that uses a shorter IV.
AES-OCB and CCM were also affected.

Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/12039)