gpio: em: use a helper variable for &pdev->dev

Instead of always dereferencing &pdev->dev, just assign a helper local
variable of type struct device * and use it where applicable.

Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>