ntb_hw_switchtec: Fix pff ioread to read into mmio_part_cfg_all

Array mmio_part_cfg_all holds the partition configuration of all
partitions, with partition number as index. Fix this by reading into
mmio_part_cfg_all for pff.

Fixes: 0ee28f26 ("NTB: switchtec_ntb: Add link management")
Signed-off-by: Jeremy Pallotta <jmpallotta@gmail.com>
Signed-off-by: Kelvin Cao <kelvin.cao@microchip.com>
Signed-off-by: Jon Mason <jdmason@kudzu.us>