greybus: gpio-gb: allow it to build properly for all current kernel versions.

GPIO remove changed the api for 3.17 to try to make up for some
previously foolish design decisions.  Handle that in kernel_ver.h to
make the code simple.
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>

drivers/staging/greybus/gpio-gb.c

@@ -799,12 +799,11 @@ int gb_gpio_controller_init(struct gb_connection *connection)
 void gb_gpio_controller_exit(struct gb_connection *connection)
 {
 	struct gb_gpio_controller *gb_gpio_controller = connection->private;
-	int ret;
 
 	if (!gb_gpio_controller)
 		return;
 
-	ret = gpiochip_remove(&gb_gpio_controller->chip);
+	gb_gpiochip_remove(&gb_gpio_controller->chip);
 	/* kref_put(gb_gpio_controller->connection) */
 	kfree(gb_gpio_controller);
 }

drivers/staging/greybus/kernel_ver.h

@@ -26,4 +26,26 @@
 #define U16_MAX	((u16)(~0U))
 #endif /* !U16_MAX */
 
+/*
+ * The GPIO api sucks rocks in places, like removal, so work around their
+ * explicit requirements of catching the return value for kernels older than
+ * 3.17, which they explicitly changed in the 3.17 kernel.  Consistency is
+ * overrated.
+ */
+#include <linux/version.h>
+#include <linux/gpio.h>
+
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0)
+static inline void gb_gpiochip_remove(struct gpio_chip *chip)
+{
+	gpiochip_remove(chip);
+}
+#else
+static inline void gb_gpiochip_remove(struct gpio_chip *chip)
+{
+	int ret;
+	ret = gpiochip_remove(chip);
+}
+#endif
+
 #endif	/* __GREYBUS_KERNEL_VER_H */