gpio: gpio-altera: Add missing kerneldoc entry and demote comment

'struct altera_gpio_chip's 'irq_chip' property is undocumented.  So
add property description to the struct's kerneldoc header.  Also
demote comment block which is clearly not in kerneldoc format.

Fixes the following W=1 warnings:

 drivers/gpio/gpio-altera.c:34: warning: Function parameter or member 'irq_chip' not described in 'altera_gpio_chip'
 drivers/gpio/gpio-altera.c:78: warning: Function parameter or member 'd' not described in 'altera_gpio_irq_set_type'
 drivers/gpio/gpio-altera.c:78: warning: Function parameter or member 'type' not described in 'altera_gpio_irq_set_type'
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Cc: Joyce Ooi <joyce.ooi@intel.com>
Cc: Tien Hock Loh <thloh@altera.com>
Link: https://lore.kernel.org/r/20200630133345.2232932-3-lee.jones@linaro.orgSigned-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpio-altera.c

@@ -24,6 +24,7 @@
 * @interrupt_trigger	: specifies the hardware configured IRQ trigger type
 *			  (rising, falling, both, high)
 * @mapped_irq		: kernel mapped irq number.
+* @irq_chip		: IRQ chip configuration
 */
 struct altera_gpio_chip {
 	struct of_mm_gpio_chip mmchip;
@@ -69,7 +70,7 @@ static void altera_gpio_irq_mask(struct irq_data *d)
 	raw_spin_unlock_irqrestore(&altera_gc->gpio_lock, flags);
 }
 
-/**
+/*
  * This controller's IRQ type is synthesized in hardware, so this function
  * just checks if the requested set_type matches the synthesized IRQ type
  */