AR9330/AR9331 also needs to ACK the APB interrupt register, same as

AR724x.

This fixes 'stuck interrupt' problems I was having when writing the
uart interrupt code.

sys/mips/atheros/apb.c

@@ -357,6 +357,8 @@ apb_filter(void *arg)
 			case AR71XX_SOC_AR7240:
 			case AR71XX_SOC_AR7241:
 			case AR71XX_SOC_AR7242:
+			case AR71XX_SOC_AR9330:
+			case AR71XX_SOC_AR9331:
 				/* Ack/clear the irq on status register for AR724x */
 				ATH_WRITE_REG(AR71XX_MISC_INTR_STATUS,
 				    reg & ~(1 << irq));