ssl_tls: fix guards for accelerated ECDH

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index a6129da..c91a12f 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -4220,7 +4220,7 @@
     mbedtls_ssl_buffering_free(ssl);
 #endif /* MBEDTLS_SSL_PROTO_DTLS */
 
-#if defined(MBEDTLS_ECDH_C) && \
+#if defined(MBEDTLS_PK_CAN_ECDH) && \
     (defined(MBEDTLS_USE_PSA_CRYPTO) || defined(MBEDTLS_SSL_PROTO_TLS1_3))
     if (handshake->ecdh_psa_privkey_is_external == 0) {
         psa_destroy_key(handshake->ecdh_psa_privkey);