vfio/pci: drop nth_page() usage within SG entry

vfio/pci: drop nth_page() usage within SG entry

It's no longer required to use nth_page() when iterating pages within a
single SG entry, so let's drop the nth_page() usage.

Link: https://lkml.kernel.org/r/20250901150359.867252-33-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Alex Williamson <alex.williamson@redhat.com>
Reviewed-by: Brett Creeley <brett.creeley@amd.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Yishai Hadas <yishaih@nvidia.com>
Cc: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>
Cc: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>