RDMA/usnic: Use iommu_paging_domain_alloc()

usnic_uiom_alloc_pd() allocates a paging domain for a given device.
In this case, iommu_domain_alloc(dev->bus) is equivalent to 
iommu_paging_domain_alloc(dev). Replace it as iommu_domain_alloc()
has been deprecated.

Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Acked-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/20240610085555.88197-15-baolu.lu@linux.intel.com


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