pinctrl: fix example .get_group_pins implementation signature

The callback function signature has changed in commit a5818a8 (pinctrl:
get_group_pins() const fixes)

Fixes: a5818a8 ('pinctrl: get_group_pins() const fixes')
Cc: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

Documentation/pinctrl.txt

@@ -163,8 +163,8 @@ static const char *foo_get_group_name(struct pinctrl_dev *pctldev,
 }
 
 static int foo_get_group_pins(struct pinctrl_dev *pctldev, unsigned selector,
-			       unsigned ** const pins,
-			       unsigned * const num_pins)
+			       const unsigned **pins,
+			       unsigned *num_pins)
 {
 	*pins = (unsigned *) foo_groups[selector].pins;
 	*num_pins = foo_groups[selector].num_pins;