Instead of direct dereferencing the IRQ data in order to get HW IRQ number
use the irqd_to_hwirq() helper.

Fixes: 5644b66a ("Documentation: Update the recommended pattern for GPIO irqchips")
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>