Add a missing function prototype.

@@ -473,6 +473,8 @@
     tasklet_unlock_wait(&ctrl_if_rx_tasklet);
 }
 
+extern int teardown_irq(unsigned int irq, struct irqaction * old);
+
 void ctrl_if_suspend(void)
 {
     teardown_irq(ctrl_if_irq, &ctrl_if_irq_action);