gpio: ep93xx: remove unused variable

This one was left behind by a previous cleanup patch:

drivers/gpio/gpio-ep93xx.c: In function 'ep93xx_gpio_add_bank':
drivers/gpio/gpio-ep93xx.c:366:34: error: unused variable 'ic' [-Werror=unused-variable]

Fixes: 216f3736 ("gpio: ep93xx: Make irqchip immutable")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>