gpio: Properly document parent data union

Suppress a warning in the html docs by documenting these fields separately.
Signed-off-by: Joey Gouly <joey.gouly@arm.com>
Link: https://lore.kernel.org/lkml/20211027220118.71a229ab@canb.auug.org.au/
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Bartosz Golaszewski <brgl@bgdev.pl>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>

include/linux/gpio/driver.h

@@ -168,13 +168,16 @@ struct gpio_irq_chip {
 
 	/**
 	 * @parent_handler_data:
+	 *
+	 * If @per_parent_data is false, @parent_handler_data is a single
+	 * pointer used as the data associated with every parent interrupt.
+	 *
 	 * @parent_handler_data_array:
 	 *
-	 * Data associated, and passed to, the handler for the parent
-	 * interrupt. Can either be a single pointer if @per_parent_data
-	 * is false, or an array of @num_parents pointers otherwise.  If
-	 * @per_parent_data is true, @parent_handler_data_array cannot be
-	 * NULL.
+	 * If @per_parent_data is true, @parent_handler_data_array is
+	 * an array of @num_parents pointers, and is used to associate
+	 * different data for each parent. This cannot be NULL if
+	 * @per_parent_data is true.
 	 */
 	union {
 		void *parent_handler_data;