pinctrl: imx5: fix GPIO_8 pad CAN1_RXCAN configuration

3 is an invalid value for the CAN1_IPP_IND_CANRX_SELECT_INPUT
register. Set it to 2, which correctly selects the GPIO_8 pad.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>