power: supply: collie_battery: Convert to GPIO descriptors (part 2)

Finish the job started by the commit ba940ed8 ("power: supply:
collie_battery: Convert to GPIO descriptors"), i.e. convert the use
of gpio_to_irq() to gpiod_to_irq(). No functional changes intended.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>