tilepro pci: fix pci_bus.subordinate bad bombing from b918c62e

The bombing to convert pci_bus.subordinate to busn_res.end accidentally
modified a "struct pci_dev" site, causing this file not to compile.
This commit reverts that code to use dev->subordinate again.

Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>