pinctrl: imx: fix imx_pinctrl_desc initialization

Fixes: 6e408ed8 ("pinctrl: imx: fix initialization of imx_pinctrl_desc")
Reviewed-by: Vladimir Zapolskiy <vladimir_zapolskiy@mentor.com>
Reviewed-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Gary Bisson <gary.bisson@boundarydevices.com>

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