Add missing #ifdef in ecdsa.c
diff --git a/library/ecdsa.c b/library/ecdsa.c
index 57f8035..b4cdfca 100644
--- a/library/ecdsa.c
+++ b/library/ecdsa.c
@@ -342,7 +342,8 @@
     return( ret );
 }
 
-#if ! defined(POLARSSL_DEPRECATED_REMOVED)
+#if ! defined(POLARSSL_DEPRECATED_REMOVED) && \
+    defined(POLARSSL_ECDSA_DETERMINISTIC)
 int ecdsa_write_signature_det( ecdsa_context *ctx,
                                const unsigned char *hash, size_t hlen,
                                unsigned char *sig, size_t *slen,