PCI: pciehp: remove device field

The device field in the struct slot is not necessary because it is
always 0 in pciehp driver.

Acked-by: Alex Chiang <achiang@hp.com>
Signed-off-by: Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>