pinctrl: imx25: fix numbering for pins

The pin id for a given tuple listed in a fsl,pins property is calculated
by dividing the first entry (which is also a register offset) by 4.
As the first available register is at offset 0x8 and configures the pad
MX25_PAD_A10 the right id for this pin is 2. All other pins are off by
one, too.

This patch drops the definition MX25_PAD_RESERVE1 (together with its
only use) and decrements all following values by 1.

Fixes: b4a87c9b ("pinctrl: pinctrl-imx: add imx25 pinctrl driver")
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Tested-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>