pinctrl: microchip-sgpio: Put fwnode in error case during ->probe()

pinctrl: microchip-sgpio: Put fwnode in error case during ->probe()

device_for_each_child_node() bumps a reference counting of a returned variable.
We have to balance it whenever we return to the caller.

Fixes: 7e5ea974e61c ("pinctrl: pinctrl-microchip-sgpio: Add pinctrl driver for Microsemi Serial GPIO")
Cc: Lars Povlsen <lars.povlsen@microchip.com>
Signed-off-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20210606191940.29312-1-andy.shevchenko@gmail.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>