PCI: rcar: Fix bridge logic configuration accesses

The bridge logic at slot 0 only supports reads up to 0x40 and the rest of
the PCI configuration space for this slot is marked as reserved in the
manual.

Trying a read from offset 0x100 is producing an error from the bridge. With
error interrupts enabled, the following is printed:

  pci-rcar-gen2 ee0d0000.pci: error irq: status 00000014

Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Signed-off-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Simon Horman <horms+renesas@verge.net.au>