pinctrl: core: Make pinctrl_release static

'pinctrl_release' is used only in this file. Hence make it static.

Without this patch we get the following sparse error:
drivers/pinctrl/core.c:815:6: warning:
symbol 'pinctrl_release' was not declared. Should it be static?
Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/pinctrl/core.c

@@ -812,7 +812,7 @@ static void pinctrl_put_locked(struct pinctrl *p, bool inlist)
  * pinctrl_release() - release the pinctrl handle
  * @kref: the kref in the pinctrl being released
  */
-void pinctrl_release(struct kref *kref)
+static void pinctrl_release(struct kref *kref)
 {
 	struct pinctrl *p = container_of(kref, struct pinctrl, users);