MIPS: lantiq: dont register irq_chip for the irq cascade

We dont want to register the irq_chip for the MIPS IRQ cascade.

Signed-off-by: John Crispin <blogic@openwrt.org>
Patchwork: http://patchwork.linux-mips.org/patch/4230/

arch/mips/lantiq/irq.c

@@ -297,6 +297,9 @@ static int icu_map(struct irq_domain *d, unsigned int irq, irq_hw_number_t hw)
 	struct irq_chip *chip = &ltq_irq_type;
 	int i;
 
+	if (hw < MIPS_CPU_IRQ_CASCADE)
+		return 0;
+
 	for (i = 0; i < exin_avail; i++)
 		if (hw == ltq_eiu_irq[i])
 			chip = &ltq_eiu_type;