pinctrl: bcm2835: Accept fewer than expected IRQs

The downstream .dts files only request two GPIO IRQs. Truncate the
array of parent IRQs when irq_of_parse_and_map returns 0.

Signed-off-by: Phil Elwell <phil@raspberrypi.com>
Signed-off-by: Ivan T. Ivanov <iivanov@suse.de>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Link: https://lore.kernel.org/r/20210521090158.26932-1-iivanov@suse.de
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>