powerpc/iommu: Set default DMA offset in dma_dev_setup

Commit e91c2511 "powerpc/iommu: Cleanup setting of DMA base/offset"
expects that the default DMA offset is set from pnv_ioda_setup_bus_dma()
which is correct unless it is SRIOV where the code flow is different -
at the moment when pnv_ioda_setup_bus_dma() is called, PCI devices for
VFs are not created yet.

This adds missing set_dma_offset() to pnv_pci_ioda_dma_dev_setup() to
cover the case of SRIOV.

Note that we still need set_dma_offset() in pnv_ioda_setup_bus_dma() as
at the boot time pnv_pci_ioda_dma_dev_setup() is called when no PE was
created yet, this happens at the PHB fixup stage.

Fixes: e91c2511 ("powerpc/iommu: Cleanup setting of DMA base/offset")
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Reviewed-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>