The Requester ID should use the Root Port devfn and it should be always 0.
Previously we constructed the Requester ID using the *Completer* devfn,
i.e., the devfn of the Function we expect to respond to the config access.
This causes issues when accessing configuration space for devices other
than the Root Port.

Build the Requester ID using the Root Port devfn.

Tested on Ethernet adapter card with multi-functions.
Signed-off-by: Ley Foon Tan <lftan@altera.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>