Fix GCC format-signedness warnings

Signed-off-by: Kenneth Soerensen <knnthsrnsn@gmail.com>
diff --git a/tests/suites/test_suite_x509parse.function b/tests/suites/test_suite_x509parse.function
index 85ff41d..f3e83d6 100644
--- a/tests/suites/test_suite_x509parse.function
+++ b/tests/suites/test_suite_x509parse.function
@@ -237,7 +237,7 @@
     char *p = *buf;
     size_t n = *size;
 
-    ret = mbedtls_snprintf( p, n, "type : %u", san->type );
+    ret = mbedtls_snprintf( p, n, "type : %d", san->type );
     MBEDTLS_X509_SAFE_SNPRINTF;
 
     switch( san->type )