pinctrl: imx8mn: Constify imx_pinctrl_soc_info

The imx_pinctrl_soc_info structure content is never changed, so it can be
declared as 'const', like it is done on all other i.MX pinctrl drivers.

Make it 'const' in this driver too.

Signed-off-by: Fabio Estevam <festevam@gmail.com>
Reviewed-by: Dong Aisheng <aisheng.dong@nxp.com>
Link: https://lore.kernel.org/r/20210713122513.3112941-1-festevam@gmail.com


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>