selftests: vm: Fix resource leak when return error

When return on an error path, file handle need to be closed
to prevent resource leak

Signed-off-by: Ding Xiang <dingxiang@cmss.chinamobile.com>
Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>