PCI: latency timer doesn't apply to PCIe

The latency timer is read-only and hardwired to zero for all PCIe
devices, both Type 0 and Type 1, so don't bother trying to update it
and cluttering the dmesg log with meaningless "setting latency timer
to 64" messages.

Signed-off-by: Myron Stowe <myron.stowe@redhat.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>