Documentation: gpio: Fix IRQ mask and unmask examples

After switching to immutable IRQ chips for GPIO drivers the examples become
uncompilable due to wrong IRQ API, i.e. irq_desc_get_handler_data() in use.
Replace it with proper irq_data_get_irq_chip_data() call where it applies.

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>