pinctrl: st: Drop unused st_gpio_bank() function

Static inline st_gpio_bank() function is not referenced:

  pinctrl-st.c:377:19: error: unused function 'st_gpio_bank' [-Werror,-Wunused-function]

Fixes: 701016c0 ("pinctrl: st: Add pinctrl and pinconf support.")
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/20250528092201.52132-2-krzysztof.kozlowski@linaro.org


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