pinctrl/nomadik: use zero as default irq_start

The irqdomain semantics were supposed to be such that a linear
domain would be used if the passed first_irq was zero or
negative, but I got it wrong so only passing zero as first_irq
will work properly. Well, zero is NO_IRQ these days so let's
pass zero. The semantics of irqdomain_add_simple() will be
fixed in a separate patch.

Acked-by: Lee Jones <lee.jones@linaro.org>
Reported-by: Rikard Olsson <rikard.p.olsson@stericsson.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>