iommu: Fix error handling in probe_acpi_namespace_devices()

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I65QZY



--------------------------------

Fix smatch error in probe_acpi_namespace_devices().

In probe_acpi_namespace_devices(), if device_to_iommu() returns NULL,
unlock operation is needed before return.

Fixes: d6602228 ("iommu/vt-d:Add support for detecting ACPI device, in RMRR")
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>
Reviewed-by: Xiongfeng Wang <wangxiongfeng2@huawei.com>
Reviewed-by: Hanjun Guo <guohanjun@huawei.com>