powerpc virq: minor cleanups

---
Index: cell--common--4/arch/powerpc/kernel/irq.c
===================================================================

--- cell--common--4.orig/arch/powerpc/kernel/irq.c
+++ cell--common--4/arch/powerpc/kernel/irq.c

@@ -678,7 +680,7 @@
 }
 EXPORT_SYMBOL_GPL(irq_dispose_mapping);
 
-unsigned int irq_find_mapping(struct irq_host *host,
+unsigned int irq_find_mapping(const struct irq_host *host,
 			      irq_hw_number_t hwirq)
 {
 	unsigned int i;

Index: cell--common--4/include/asm-powerpc/irq.h
===================================================================

--- cell--common--4.orig/include/asm-powerpc/irq.h
+++ cell--common--4/include/asm-powerpc/irq.h

@@ -28,10 +28,10 @@
 
 #ifdef CONFIG_PPC_MERGE
 
-/* This number is used when no interrupt has been assigned */
+/* This number is used when no virq has been assigned */
 #define NO_IRQ			(0)
 
-/* This is a special irq number to return from get_irq() to tell that
+/* This is a special virq number to return from get_irq() to tell that
  * no interrupt happened _and_ ignore it (don't count it as bad). Some
  * platforms like iSeries rely on that.
  */

@@ -217,7 +222,7 @@
  * irq controller implementation directly calls the appropriate low level
  * mapping function.
  */
-extern unsigned int irq_find_mapping(struct irq_host *host,
+extern unsigned int irq_find_mapping(const struct irq_host *host,
 				     irq_hw_number_t hwirq);