Add explicit checks for non-zero result of platform setup in test suites

diff --git a/tests/suites/helpers.function b/tests/suites/helpers.function
index e716318..c436fbb 100644
--- a/tests/suites/helpers.function
+++ b/tests/suites/helpers.function
@@ -133,7 +133,7 @@
 static int platform_setup()
 {
 #if defined(MBEDTLS_PLATFORM_C)
-    if( mbedtls_platform_setup( &platform_ctx ) )
+    if( mbedtls_platform_setup( &platform_ctx ) != 0 )
     {
         return -1;
     }