powerpc: Remove virq_to_host

The only references to the irq_map[].host field are internal to
arch/powerpc/kernel/irq.c

Signed-off-by: Milton Miller <miltonm@bga.com>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/kernel/irq.c

@@ -516,12 +516,6 @@ bool virq_is_host(unsigned int virq, struct irq_host *host)
 }
 EXPORT_SYMBOL_GPL(virq_is_host);
 
-struct irq_host *virq_to_host(unsigned int virq)
-{
-	return irq_map[virq].host;
-}
-EXPORT_SYMBOL_GPL(virq_to_host);
-
 static int default_irq_host_match(struct irq_host *h, struct device_node *np)
 {
 	return h->of_node != NULL && h->of_node == np;