iommufd: Use iommu_paging_domain_alloc()

If the iommu driver doesn't implement its domain_alloc_user callback,
iommufd_hwpt_paging_alloc() rolls back to allocate an iommu paging domain.
Replace iommu_domain_alloc() with iommu_user_domain_alloc() to pass the
device pointer along the path.

Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/20240610085555.88197-3-baolu.lu@linux.intel.com


Signed-off-by: Will Deacon <will@kernel.org>