Correct sample code to avoid confusing readers.

Signed-off-by: Keqian Zhu <zhukeqian1@huawei.com>
Cc: qemu-trivial@nongnu.org
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Message-Id: <20210106071710.15836-1-zhukeqian1@huawei.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>