irqchip: sun4i: Fix irq 0 not working

{

	u32 irq, hwirq;

	/*

	 * hwirq == 0 can mean one of 3 things:

	 * 1) no more irqs pending

	 * 2) irq 0 pending

	 * 3) spurious irq

	 * So if we immediately get a reading of 0, check the irq-pending reg

	 * to differentiate between 2 and 3. We only do this once to avoid

	 * the extra check in the common case of 1 hapening after having

	 * read the vector-reg once.

	 */

	hwirq = readl(sun4i_irq_base + SUN4I_IRQ_VECTOR_REG) >> 2;

	while (hwirq != 0) {

	if (hwirq == 0 &&

		  !(readl(sun4i_irq_base + SUN4I_IRQ_PENDING_REG(0)) & BIT(0)))

		return;

	do {

		irq = irq_find_mapping(sun4i_irq_domain, hwirq);

		handle_IRQ(irq, regs);

		hwirq = readl(sun4i_irq_base + SUN4I_IRQ_VECTOR_REG) >> 2;

	}

	} while (hwirq != 0);

}