PCI: hand PCI maintenance over to Bjorn Helgaas

I find I have less and less time to manage PCI patches and so I've been
looking for a replacement.  Bjorn has been substitute maintainer several
times, and acts as de-facto maintainer for certain portions anyway.
He's kindly agreed to take over in my stead; this makes it official.

Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org.>