iommu: Remove comment of dev_has_feat in struct doc

dev_has_feat has been removed from iommu_ops in commit
309c56e8

 ("iommu: remove the unused dev_has_feat method"),
remove its description in the struct doc.

Signed-off-by: Yuan Can <yuancan@huawei.com>
Link: https://lore.kernel.org/r/20220815013339.2552-1-yuancan@huawei.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>