sh-pfc: Add function to retrieve a pin instance from its pin number

This prepares support for sparse pin numbering. The function currently
just performs and indexed lookup in the pins array.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
diff --git a/drivers/pinctrl/sh-pfc/gpio.c b/drivers/pinctrl/sh-pfc/gpio.c
index db9af4e..45090d8 100644
--- a/drivers/pinctrl/sh-pfc/gpio.c
+++ b/drivers/pinctrl/sh-pfc/gpio.c
@@ -43,8 +43,9 @@
 static int gpio_pin_request(struct gpio_chip *gc, unsigned offset)
 {
 	struct sh_pfc *pfc = gpio_to_pfc(gc);
+	struct sh_pfc_pin *pin = sh_pfc_get_pin(pfc, offset);
 
-	if (pfc->info->pins[offset].enum_id == 0)
+	if (pin->enum_id == 0)
 		return -EINVAL;
 
 	return pinctrl_request_gpio(offset);