gpiolib: Update header block in gpiolib-cdev.h

The dev_t is defined in types.h while struct gpio_device forward declaration
is missed. Take into account above and update header block in gpiolib-cdev.h.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20201005095622.73616-1-andriy.shevchenko@linux.intel.comSigned-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpiolib-cdev.h

@@ -3,7 +3,9 @@
 #ifndef GPIOLIB_CDEV_H
 #define GPIOLIB_CDEV_H
 
-#include <linux/device.h>
+#include <linux/types.h>
+
+struct gpio_device;
 
 #ifdef CONFIG_GPIO_CDEV