gpio: uapi: fix kernel-doc warnings

Fix kernel-doc warnings, specifically gpioline_info_changed.padding is
not documented and 'GPIO event types' describes defines, which are not
documented by kernel-doc.
Signed-off-by: Kent Gibson <warthog618@gmail.com>
Reviewed-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20201005070329.21055-2-warthog618@gmail.comSigned-off-by: Linus Walleij <linus.walleij@linaro.org>

include/uapi/linux/gpio.h

@@ -346,6 +346,7 @@ enum {
  * @timestamp: estimate of time of status change occurrence, in nanoseconds
  * @event_type: one of GPIOLINE_CHANGED_REQUESTED, GPIOLINE_CHANGED_RELEASED
  * and GPIOLINE_CHANGED_CONFIG
+ * @padding: reserved for future use
  *
  * Note: struct gpioline_info embedded here has 32-bit alignment on its own,
  * but it works fine with 64-bit alignment too. With its 72 byte size, we can
@@ -469,7 +470,7 @@ struct gpioevent_request {
 	int fd;
 };
 
-/**
+/*
  * GPIO event types
  */
 #define GPIOEVENT_EVENT_RISING_EDGE 0x01