drm/nouveau/nouveau: fix page fault on device private memory

drm/nouveau/nouveau: fix page fault on device private memory

If system memory is migrated to device private memory and no GPU MMU
page table entry exists, the GPU will fault and call hmm_range_fault()
to get the PFN for the page. Since the .dev_private_owner pointer in
struct hmm_range is not set, hmm_range_fault returns an error which
results in the GPU program stopping with a fatal fault.
Fix this by setting .dev_private_owner appropriately.

Fixes: 08ddddda667b ("mm/hmm: check the device private page owner in hmm_range_fault()")
Cc: stable@vger.kernel.org
Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>
Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>