PCI: rcar-gen2: Make of_device_ids const

of_device_ids are not supposed to change at runtime.  All functions working
with of_device_ids provided by <linux/of.h> work with const of_device_ids.
So mark the non-const structs as const.

Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Simon Horman <horms+renesas@verge.net.au>
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>