vfio: use vfio_pci_core_setup_barmap to map bar in mmap

vfio: use vfio_pci_core_setup_barmap to map bar in mmap

Remove code duplication in vfio_pci_core_mmap by calling
vfio_pci_core_setup_barmap to perform the bar mapping.

No functional change is intended.

Cc: Donald Dutile <ddutile@redhat.com>
Reviewed-by: Shameer Kolothum <skolothumtho@nvidia.com>
Reviewed-by: Zhi Wang <zhiw@nvidia.com>
Suggested-by: Alex Williamson <alex@shazbot.org>
Signed-off-by: Ankit Agrawal <ankita@nvidia.com>
Link: https://lore.kernel.org/r/20251127170632.3477-4-ankita@nvidia.com
Signed-off-by: Alex Williamson <alex@shazbot.org>