[POWERPC] Check for NULL ppc_md.init_IRQ() before calling

Check to make sure ppc_md.init_IRQ has been set before calling it.

Signed-off-by: Sonny Rao <sonny@burdell.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>
diff --git a/arch/powerpc/kernel/irq.c b/arch/powerpc/kernel/irq.c
index a335156..2fc8786 100644
--- a/arch/powerpc/kernel/irq.c
+++ b/arch/powerpc/kernel/irq.c
@@ -336,7 +336,8 @@
 
 void __init init_IRQ(void)
 {
-	ppc_md.init_IRQ();
+	if (ppc_md.init_IRQ)
+		ppc_md.init_IRQ();
 #ifdef CONFIG_PPC64
 	irq_ctx_init();
 #endif