pinctrl: bcm2835: fix build warning in bcm2835_gpio_irq_handle_bank

This patch fix the following build warning:
drivers/pinctrl/bcm/pinctrl-bcm2835.c:376:15: warning: variable 'type' set but not used [-Wunused-but-set-variable]

Furthermore, it is unused for a long time, at least since commit 85ae9e51 ("pinctrl: bcm2835: switch to GPIOLIB_IRQCHIP")
where a "FIXME no clue why the code looks up the type here" was added.
A year after, nobody answeered this question, so its time to remove it.

Signed-off-by: Corentin Labbe <clabbe.montjoie@gmail.com>
Acked-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>