iommu: dev_bypass: cleanup dev bypass code

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I41AUQ


CVE: NA

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The device bypass code can be cleanuped to be more readable.

Signed-off-by: Hanjun Guo <guohanjun@huawei.com>
Cc: Guo Hui <guohui@uniontech.com>
Cc: Cheng Jian <cj.chengjian@huawei.com>
Cc: Zhen Lei <thunder.leizhen@huawei.com>
Cc: Xiuqi Xie <xiexiuqi@huawei.com>
Reviewed-by: Xie XiuQi <xiexiuqi@huawei.com>
Signed-off-by: Cheng Jian <cj.chengjian@huawei.com>