Fix incorrect error message

Signed-off-by: Paul Elliott <paul.elliott@arm.com>
diff --git a/library/ssl_tls12_server.c b/library/ssl_tls12_server.c
index 8e0ec6a..05a5767 100644
--- a/library/ssl_tls12_server.c
+++ b/library/ssl_tls12_server.c
@@ -2858,7 +2858,7 @@
     const mbedtls_pk_context *private_key = mbedtls_ssl_own_key( ssl );
     if( private_key == NULL)
     {
-        MBEDTLS_SSL_DEBUG_MSG( 1, ( "got no ECDH private key" ) );
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "got no server private key" ) );
         return( MBEDTLS_ERR_SSL_PRIVATE_KEY_REQUIRED );
     }