gpio: rcar: Always use local variable dev in gpio_rcar_probe()

As we have already have a pointer to the device structure in a local
variable in gpio_rcar_probe(), we can just use "dev" instead of
"p->dev".

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>