gpio: consumer.h: Move forward declarations outside #ifdef

Make sure that the forward declared structs in gpio/consumer.h are also visible
on the else branch of the CONFIG_GPIOLIB #ifdef.

Fixes the following warnings and their associated errors when CONFIG_GPIOLIB is
not selected:
	include/linux/gpio/consumer.h:67:14: warning: 'struct device' declared inside parameter list
	include/linux/gpio/consumer.h:67:14: warning: its scope is only this definition or declaration, which is probably not what you want
	[...]
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

include/linux/gpio/consumer.h

@@ -4,8 +4,6 @@
 #include <linux/err.h>
 #include <linux/kernel.h>
 
-#ifdef CONFIG_GPIOLIB
-
 struct device;
 struct gpio_chip;
 
@@ -18,6 +16,8 @@ struct gpio_chip;
  */
 struct gpio_desc;
 
+#ifdef CONFIG_GPIOLIB
+
 /* Acquire and dispose GPIOs */
 struct gpio_desc *__must_check gpiod_get(struct device *dev,
 					 const char *con_id);