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

diff --git a/tests/suites/main_test.function b/tests/suites/main_test.function
index e5b4043..8d7e477 100644
--- a/tests/suites/main_test.function
+++ b/tests/suites/main_test.function
@@ -282,7 +282,7 @@
     !defined(TEST_SUITE_MEMORY_BUFFER_ALLOC)
     unsigned char alloc_buf[1000000];
 #endif 
-    if( platform_setup() )
+    if( platform_setup() != 0 )
     {
         mbedtls_fprintf( stderr, "FATAL: Failed to initialize platform" );
         return -1;