Adapt guards for FFDH

Signed-off-by: Przemek Stekiel <przemyslaw.stekiel@mobica.com>
diff --git a/library/ssl_tls13_generic.c b/library/ssl_tls13_generic.c
index feca203..6a1006f 100644
--- a/library/ssl_tls13_generic.c
+++ b/library/ssl_tls13_generic.c
@@ -1488,7 +1488,7 @@
     return ret;
 }
 
-#if defined(PSA_WANT_ALG_ECDH)
+#if defined(PSA_WANT_ALG_ECDH) || defined(PSA_WANT_ALG_FFDH)
 
 int mbedtls_ssl_tls13_read_public_ecdhe_share(mbedtls_ssl_context *ssl,
                                               const unsigned char *buf,
@@ -1569,7 +1569,7 @@
 
     return 0;
 }
-#endif /* PSA_WANT_ALG_ECDH */
+#endif /* PSA_WANT_ALG_ECDH || PSA_WANT_ALG_FFDH */
 
 #if defined(PSA_WANT_ALG_FFDH)
 int mbedtls_ssl_tls13_generate_and_write_dhe_key_exchange(