pinctrl: amd: fix compilation warning

3bfd44306c65 ("pinctrl: amd: Add support for additional GPIO")
created the following warning:

drivers/pinctrl/pinctrl-amd.c: In function 'amd_gpio_dbg_show':
drivers/pinctrl/pinctrl-amd.c:210:3: warning: 'pin_num' may be used uninitialized in this function [-Wmaybe-uninitialized]
   for (; i < pin_num; i++) {
   ^
drivers/pinctrl/pinctrl-amd.c:172:21: warning: 'i' may be used uninitialized in this function [-Wmaybe-uninitialized]
  unsigned int bank, i, pin_num;
                     ^
Fix this by adding a guarding default case for illegal
bank numbers.

Cc: S-k Shyam-sundar <Shyam-sundar.S-k@amd.com>
Cc: Nehal Shah <Nehal-bakulchandra.Shah@amd.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/pinctrl/pinctrl-amd.c

@@ -206,6 +206,9 @@ static void amd_gpio_dbg_show(struct seq_file *s, struct gpio_chip *gc)
 			i = 192;
 			pin_num = AMD_GPIO_PINS_BANK3 + i;
 			break;
+		default:
+			/* Illegal bank number, ignore */
+			continue;
 		}
 		for (; i < pin_num; i++) {
 			seq_printf(s, "pin%d\t", i);