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: 701016c0cba5 ("pinctrl: st: Add pinctrl and pinconf support.")
Signed-off-by: Krzysztof Kozlowski <[e-mail]>
Link: https://lore.kernel.org/[e-mail]
Signed-off-by: Linus Walleij <[e-mail]>

drivers/pinctrl/pinctrl-st.c

···
 }
 
 /* Low level functions.. */
-static inline int st_gpio_bank(int gpio)
-{
-	return gpio/ST_GPIO_PINS_PER_BANK;
-}
-
 static inline int st_gpio_pin(int gpio)
 {
 	return gpio%ST_GPIO_PINS_PER_BANK;