fetch macctx while fetching digest when creating HMAC-DRBG

Somewhere in our conversion from .c files to .inc files for our rand
providers, we created code in drbg_hmac_set_ctx_params_locked to fetch
our digest and hmac when creating the rand instance.  However, the
function drbg_fetch_algs_from_prov only fetched our digest for this rand
type, not the hmac, and returned 1 while doing so, indicating success.
This is problematic because it means that we never wind up fetching an
HMAC for this rand type.  As a result we never compute the strength of
the DRBG and so any attempt to seed it fails.

Ensure that, if we load a digest for this DRBG, we also fetch an HMAC,
and fail if we can't do so, so the HMAC-DRBG is useful.

Fixes openssl/private#853

Reviewed-by: Eugene Syromiatnikov <esyr@openssl.org>
Reviewed-by: Paul Dale <paul.dale@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/29569)

providers/implementations/rands/drbg_hmac.c.in

@@ -524,6 +524,10 @@ static int drbg_hmac_set_ctx_params_locked(PROV_DRBG *ctx, const struct drbg_set
         (void)ERR_clear_last_mark();
         if (prov_md)
             ossl_prov_digest_set_md(&hmac->digest, prov_md);
+        if (!ossl_prov_macctx_load(&hmac->ctx, p->mac, NULL, p->digest,
+                p->propq, p->engine,
+                NULL, NULL, NULL, libctx))
+            return 0;
     }
 
     md = ossl_prov_digest_md(&hmac->digest);