PCI: rcar: Use of_device_get_match_data() to simplify probe

This is a DT-only driver, so the only way to call rcar_pcie_probe() is to
match an entry in rcar_pcie_of_match[], so of_id cannot be NULL.

Furthermore, of_id->data can only be NULL if an rcar_pcie_of_match[] entry
has a NULL .data member.  That's a driver defect, and we don't want to
return -EINVAL, which is easy to ignore.  We'd rather take the NULL pointer
dereference so we notice the problem and fix it.

Use of_device_get_match_data() to retrieve the hw_init_fn pointer.  No
functional change intended.

Suggested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Simon Horman <horms+renesas@verge.net.au>