of/irq: init struct resource to 0 in of_irq_to_resource()

It almost does not matter because most users use only the ->start member
of the struct. However if this struct is passed to a platform device
which is then added via platform_device_add() then the ->parent member is
also used.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Grant Likely <grant.likely@linaro.org>