pinctrl: stm32: use valid pin identifier in stm32_pinctrl_resume()

When resuming from low power, the driver attempts to restore the
configuration of some pins. This is done by a call to:
  stm32_pinctrl_restore_gpio_regs(struct stm32_pinctrl *pctl, u32 pin)
where 'pin' must be a valid pin value (i.e. matching some 'groups->pin').
Fix the current implementation which uses some wrong 'pin' value.

Fixes: e2f3cf18 ("pinctrl: stm32: add suspend/resume management")
Signed-off-by: Fabien Dessenne <fabien.dessenne@foss.st.com>
Link: https://lore.kernel.org/r/20211008122517.617633-1-fabien.dessenne@foss.st.com


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