PCI/DPC: Remove rp_pio_status from dpc struct

We don't need to save the rp pio status across multiple contexts as all
DPC event handling occurs in a single work queue context.

Signed-off-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Sinan Kaya <okaya@kernel.org>
Reviewed-by: Oza Pawandeep <poza@codeaurora.org>