pinctrl: mediatek: Fix pinctrl register irq fail bug.

Since mt6397 is no need to support interrupt controller,
I judged "interrupt-controller" property to skip it last patch.
But the if judgement should on the contrary, this is a bug.

And find of_property_read_bool is better for this case.
So using of_property_read_bool instead of of_find_property.

Also fix bug of misuse pointer.

Signed-off-by: Hongzhou Yang <hongzhou.yang@mediatek.com>
Reviewed-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>