load_roots: fix no-argument detection

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/programs/x509/load_roots.c b/programs/x509/load_roots.c
index de9914e..69357ff 100644
--- a/programs/x509/load_roots.c
+++ b/programs/x509/load_roots.c
@@ -136,7 +136,7 @@
     struct mbedtls_timing_hr_time timer;
     unsigned long ms;
 
-    if( argc == 0 )
+    if( argc <= 1 )
     {
         mbedtls_printf( USAGE );
         goto exit;