Add missing ifdefs

Make sure that the error translating functions
are only defined when they're used.
Signed-off-by: Andrzej Kurek <andrzej.kurek@arm.com>
diff --git a/library/ssl_tls12_server.c b/library/ssl_tls12_server.c
index d29aa8d..03f9eea 100644
--- a/library/ssl_tls12_server.c
+++ b/library/ssl_tls12_server.c
@@ -36,6 +36,8 @@
 #if defined(MBEDTLS_USE_PSA_CRYPTO)
 /* Define a local translating function to save code size by not using too many
  * arguments in each translating place. */
+#if defined(MBEDTLS_KEY_EXCHANGE_SOME_ECDH_ENABLED) || \
+    defined(MBEDTLS_KEY_EXCHANGE_SOME_ECDHE_ENABLED)
 static int local_err_translation(psa_status_t status)
 {
     return psa_status_to_mbedtls(status, psa_to_ssl_errors,
@@ -44,6 +46,7 @@
 }
 #define PSA_TO_MBEDTLS_ERR(status) local_err_translation(status)
 #endif
+#endif
 
 #if defined(MBEDTLS_ECP_C)
 #include "mbedtls/ecp.h"