parisc/PCI: Enable PERR/SERR on all devices

Previously, we enabled PERR & SERR for the first device on the bus, but
left other devices alone.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Yinghai Lu <yinghai@kernel.org>
CC: linux-parisc@vger.kernel.org