genirq: fix off by one and coding style

Fix off-by-one in for_each_irq_desc_reverse().

Impact is near zero in practice, because nothing substantial wants to
iterate down to IRQ#0 - but fix it nevertheless.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
diff --git a/include/linux/irqnr.h b/include/linux/irqnr.h
index 3171ddc..452c280 100644
--- a/include/linux/irqnr.h
+++ b/include/linux/irqnr.h
@@ -13,9 +13,9 @@
 # define for_each_irq_desc(irq, desc)		\
 	for (irq = 0, desc = irq_desc; irq < nr_irqs; irq++, desc++)
 
-# define for_each_irq_desc_reverse(irq, desc)			\
-	for (irq = nr_irqs -1, desc = irq_desc + (nr_irqs -1 );	\
-	     irq > 0; irq--, desc--)
+# define for_each_irq_desc_reverse(irq, desc)				\
+	for (irq = nr_irqs - 1, desc = irq_desc + (nr_irqs - 1);	\
+	     irq >= 0; irq--, desc--)
 #endif
 
 #define for_each_irq_nr(irq)			\