Fix mismatch of OpenSSL function signatures that cause errors with gc…

…c-14

Building with gcc-14 fails with diagnostics like this:

```
src/tpm2-tss-engine-rsa.c:805:46: error: passing argument 2 of 'EVP_PKEY_meth_set_copy' from incompatible pointer type [-Wincompatible-pointer-types]
  805 |     EVP_PKEY_meth_set_copy(pkey_rsa_methods, rsa_pkey_copy);
      |                                              ^~~~~~~~~~~~~
      |                                              |
      |                                              int (*)(EVP_PKEY_CTX *, EVP_PKEY_CTX *) {aka int (*)(struct evp_pkey_ctx_st *, struct evp_pkey_ctx_st *)}
/usr/include/openssl/evp.h:2005:36: note: expected 'int (*)(EVP_PKEY_CTX *, const EVP_PKEY_CTX *)' {aka 'int (*)(struct evp_pkey_ctx_st *, const struct evp_pkey_ctx_st *)'} but argument is of type 'int (*)(EVP_PKEY_CTX *, EVP_PKEY_CTX *)' {aka 'int (*)(struct evp_pkey_ctx_st *, struct evp_pkey_ctx_st *)'}
```

A look into OpenSSL upstream shows that these functions have always had const
`src` parameters. Thus this error was simply not detected by earlier compiler
versions.

src/tpm2-tss-engine-ecc.c

@@ -52,7 +52,7 @@ EC_KEY_METHOD *ecc_methods = NULL;
 #endif /* OPENSSL_VERSION_NUMBER < 0x10100000 */
 
 #ifdef HAVE_OPENSSL_DIGEST_SIGN
-static int (*ecdsa_pkey_orig_copy)(EVP_PKEY_CTX *dst, EVP_PKEY_CTX *src);
+static int (*ecdsa_pkey_orig_copy)(EVP_PKEY_CTX *dst, const EVP_PKEY_CTX *src);
 static void (*ecdsa_pkey_orig_cleanup)(EVP_PKEY_CTX *ctx);
 #endif /* HAVE_OPENSSL_DIGEST_SIGN */
 
@@ -405,7 +405,7 @@ ecdsa_ec_key_sign(const unsigned char *dgst, int dgst_len, const BIGNUM *inv,
 
 #ifdef HAVE_OPENSSL_DIGEST_SIGN
 static int
-ecdsa_pkey_copy(EVP_PKEY_CTX *dst, EVP_PKEY_CTX *src)
+ecdsa_pkey_copy(EVP_PKEY_CTX *dst, const EVP_PKEY_CTX *src)
 {
     if (ecdsa_pkey_orig_copy && !ecdsa_pkey_orig_copy(dst, src))
         return 0;

src/tpm2-tss-engine-rsa.c

@@ -49,7 +49,7 @@ RSA_METHOD *rsa_methods = NULL;
 #endif /* OPENSSL_VERSION_NUMBER < 0x10100000 */
 
 #ifdef HAVE_OPENSSL_DIGEST_SIGN
-static int (*rsa_pkey_orig_copy)(EVP_PKEY_CTX *dst, EVP_PKEY_CTX *src);
+static int (*rsa_pkey_orig_copy)(EVP_PKEY_CTX *dst, const EVP_PKEY_CTX *src);
 static void (*rsa_pkey_orig_cleanup)(EVP_PKEY_CTX *ctx);
 #endif /* HAVE_OPENSSL_DIGEST_SIGN */
 
@@ -637,7 +637,7 @@ RSA_METHOD rsa_methods = {
 
 #ifdef HAVE_OPENSSL_DIGEST_SIGN
 static int
-rsa_pkey_copy(EVP_PKEY_CTX *dst, EVP_PKEY_CTX *src)
+rsa_pkey_copy(EVP_PKEY_CTX *dst, const EVP_PKEY_CTX *src)
 {
     if (rsa_pkey_orig_copy && !rsa_pkey_orig_copy(dst, src))
         return 0;