pinctrl: stm32: Unshadow np variable in stm32_pctl_probe()

pinctrl: stm32: Unshadow np variable in stm32_pctl_probe()

The np variable is used globally for stm32_pctl_probe() and in one of
its code branches. cppcheck is not happy with that:

  pinctrl-stm32.c:1530:23: warning: Local variable 'np' shadows outer variable [shadowVariable]

Instead of simply renaming one of the variables convert some code to
use a device pointer directly.

Fixes: bb949ed9b16b ("pinctrl: stm32: Switch to use for_each_gpiochip_node() helper")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Fabien Dessenne <fabien.dessenne@foss.st.com>
Link: https://lore.kernel.org/r/20220507102257.26414-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>