pinctrl: stm32: fix array read out of bound

The existing code does not verify if the "tentative" index exceeds
the size of the array, causing out of bound read.
Issue identified with kasan.

Check the index before using it.
Signed-off-by: Antonio Borneo <antonio.borneo@foss.st.com>
Fixes: 32c170ff ("pinctrl: stm32: set default gpio line names using pin names")
Link: https://lore.kernel.org/r/20231107110520.4449-1-antonio.borneo@foss.st.comSigned-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/pinctrl/stm32/pinctrl-stm32.c

@@ -1273,9 +1273,11 @@ static struct stm32_desc_pin *stm32_pctrl_get_desc_pin_from_gpio(struct stm32_pi
 	int i;
 
 	/* With few exceptions (e.g. bank 'Z'), pin number matches with pin index in array */
-	pin_desc = pctl->pins + stm32_pin_nb;
-	if (pin_desc->pin.number == stm32_pin_nb)
-		return pin_desc;
+	if (stm32_pin_nb < pctl->npins) {
+		pin_desc = pctl->pins + stm32_pin_nb;
+		if (pin_desc->pin.number == stm32_pin_nb)
+			return pin_desc;
+	}
 
 	/* Otherwise, loop all array to find the pin with the right number */
 	for (i = 0; i < pctl->npins; i++) {