iommu: Remove __iommu_group_for_each_dev()

The last two users of it are quite trivial, just open code the one line
loop.

Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
Tested-by: Heiko Stuebner <heiko@sntech.de>
Tested-by: Niklas Schnelle <schnelle@linux.ibm.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/16-v5-1b99ae392328+44574-iommu_err_unwind_jgg@nvidia.com


Signed-off-by: Joerg Roedel <jroedel@suse.de>