gpio: rcar: Remove #gpio-range-cells DT property usage

Commit a1bc260b ("gpio: clean up
gpio-ranges documentation") deprecated the #gpio-range-cells property.
Replace its usage with a hardcoded value in the gpio-rcar driver.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>