onda:  fix compiler warning in boot loader

Change-Id: Ic92d8e183503b68604d69bad27991f66d89c8744
diff --git a/bootloader/ondavx747.c b/bootloader/ondavx747.c
index 0f1c504..cdacb69 100644
--- a/bootloader/ondavx747.c
+++ b/bootloader/ondavx747.c
@@ -252,6 +252,7 @@
     else
         poweroff_repeat = 0;
     }
+    return 0;
 }
 
 int main(void)