pinctrl: header: trivial: declare struct device

As struct device is used as a function argument, it should at
least be declared (device.h is not included).
Signed-off-by: Richard Genoud <richard.genoud@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

include/linux/pinctrl/consumer.h

@@ -20,6 +20,7 @@
 /* This struct is private to the core and should be regarded as a cookie */
 struct pinctrl;
 struct pinctrl_state;
+struct device;
 
 #ifdef CONFIG_PINCTRL