pinctrl: imx25: ensure that a pin with id i is at position i in the info array

The code in pinctrl-imx.c only works correctly if in the
imx_pinctrl_soc_info passed to imx_pinctrl_probe we have:

	info->pins[i].number = i
	conf_reg(info->pins[i]) = 4 * i

(which conf_reg(pin) being the offset of the pin's configuration
register).

When the imx25 specific part was introduced in b4a87c9b ("pinctrl:
pinctrl-imx: add imx25 pinctrl driver") we had:

	info->pins[i].number = i + 1
	conf_reg(info->pins[i]) = 4 * i

. Commit 34027ca2 ("pinctrl: imx25: fix numbering for pins") tried
to fix that but made the situation:

	info->pins[i-1].number = i
	conf_reg(info->pins[i-1]) = 4 * i

which is hardly better but fixed the error seen back then.

So insert another reserved entry in the array to finally yield:

	info->pins[i].number = i
	conf_reg(info->pins[i]) = 4 * i

Fixes: 34027ca2 ("pinctrl: imx25: fix numbering for pins")
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>