tests/unit/test-smp-parse: Explicit MachineClass name

tests/unit/test-smp-parse: Explicit MachineClass name

If the MachineClass::name pointer is not explicitly set, it is NULL.
Per the C standard, passing a NULL pointer to printf "%s" format is
undefined. Some implementations display it as 'NULL', other as 'null'.
Since we are comparing the formatted output, we need a stable value.
The easiest is to explicit a machine name string.

Reviewed-by: Andrew Jones <drjones@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Yanan Wang <wangyanan55@huawei.com>
Tested-by: Yanan Wang <wangyanan55@huawei.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20211115145900.2531865-4-philmd@redhat.com>