Fix errors found by parfait static analyser.

Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/15579)

crypto/evp/kdf_lib.c

@@ -125,7 +125,7 @@ void EVP_KDF_CTX_reset(EVP_KDF_CTX *ctx)
 size_t EVP_KDF_CTX_get_kdf_size(EVP_KDF_CTX *ctx)
 {
     OSSL_PARAM params[2] = { OSSL_PARAM_END, OSSL_PARAM_END };
-    size_t s;
+    size_t s = 0;
 
     if (ctx == NULL)
         return 0;

providers/implementations/macs/cmac_prov.c

@@ -87,6 +87,8 @@ static void *cmac_dup(void *vsrc)
         return NULL;
 
     dst = cmac_new(src->provctx);
+    if (dst == NULL)
+        return NULL;
     if (!CMAC_CTX_copy(dst->ctx, src->ctx)
         || !ossl_prov_cipher_copy(&dst->cipher, &src->cipher)) {
         cmac_free(dst);