iommu: Fix comment for struct iommu_fwspec

iommu: Fix comment for struct iommu_fwspec

Commit 986d5ecc5699 ("iommu: Move fwspec->iommu_priv to struct
dev_iommu") removed iommu_priv from fwspec and commit 5702ee24182f
("ACPI/IORT: Check ATS capability in root complex nodes") added @flags.
Update the struct doc.

Acked-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Acked-by: Will Deacon <will@kernel.org>
Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
Link: https://lore.kernel.org/r/20210401154718.307519-2-jean-philippe@linaro.org
Signed-off-by: Joerg Roedel <jroedel@suse.de>