gpio: max77620: Remove unused fields from struct max77620_gpio

Current code does not use gpio_irq/irq_base/gpio_base fields from
struct max77620_gpio, so remove them.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Acked-by: Laxman Dewangan <ldewangan@nvidia.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>